How the Game Works
The netrek universe is a strange one, and works in ways which are in some cases counter-intuitive. This section describes some of those workings.
The way ships move in netrek is not very "realistic". They steer more like cars or boats, always moving the same way they face. When you click (or hit k) to indicate desired direction, your ship begins to turn to face that way. A ship's turning speed depends on its type (smaller ships turn faster) and its current speed. Each extra warp speed you travel halves your turning rate. So slow down when you need to turn! Acceleration and deceleration rates are also ship-dependent.
Ships can pass through each other without harm. Also ships can pass over planets, but will suffer some damage from "planetary fire" from hostile planets. Torpedos and other weapons are not affected by planets (or vice versa). Ships bounce off the walls at the edge of the galaxy without harm.
Torpedos move through the "ether" at a constant speed, more like they would in water than space. Torpedo speed is warp 12 for cruiser and battleship torpedos, warp 14 for destroyer and starbase torpedos, and warp 16 for scout and assault ship torpedos. Torpedos wobble randomly a bit as they go, and peter out after traveling a somewhat random distance. Torpedos pass right through ships on the same team, but explode on impact with hostile ships. By "on impact" I just mean when they get close enough--about shield radius, the same distance for all ship-types and the same whether shields are up or down. Torpedos also explode upon hitting the galaxy wall, and upon being detonated by a nearby enemy (but not when aborted by the ship that fired them). The normal case is when a torpedo hits a hostile ship, and depending on the firing ship's type it will do 40 (CA, BB), 30 (DD, AS, SB), or 25 (SC) points of damage. But if there are other ships nearby when the torpedo explodes, they'll take damage as well, except that the firing ship is immune to its own torpedos. If a torpedo is detonated by a hostile ship, its explosion will not hurt teammates of the detonating ship, but can hurt nearby teammates of the firing ship. If a torpedo explodes by hitting the wall, it can hurt enemies but not friends. When a ship takes damage from a torpedo explosion at all, the damage depends on the ship's distance from the explosion. At maximum detonation range torpedos do about 1/8 of their nominal damage.
When your ship is destroyed, you get to re-enter with a new ship (of your choice) near your homeworld. If you had torpedos in the air you have to wait for them to explode or expire. Ships explode when they die, damaging all other ships within a certain radius (the damage drops off with distance). SB explosions do 200, SC explosions do 75, all others do 100.
When you kill an enemy ship you are awarded 1 kill, plus 0.1 per kill that ship had, plus 0.1 per army that ship carried. Ships can carry two armies per kill (or 3 per kill for assault ships), up to their maximum capacity (2 for SC, 5 for DD, 10 for CA, 6 for BB, 20 for AS). When you die you lose your kills. You also get 0.25 kills for taking a planet, and 0.02 kills per army bombed.
Cloaked ships don't appear on the tactical display, but normally show up as ?? on the galactic map. Under certain circumstances a cloaked ship won't register on enemy maps at all, namely when it is out of yellow-alert range (1/7 galaxy width) from any enemy, not orbiting a hostile or 3rd-race planet, and in t-mode. Actually change that 1/7 to a 1/3, and those are the conditions under which an uncloaked ship won't register on enemy maps either. When the ?? is shown, its position is randomly offset from the actually position of the ship.
You cannot fire weapons or use tractor/pressor beams while cloaked, but you can do many other things, including bombing, beaming armies, toggling shields, detonating torpedos, and repairing. Cloaking costs a fair amount of fuel per second though. Uncloaking takes 0.7 seconds, and you can't fire weapons until you come completely uncloaked. But you can tractor or pressor as soon as you start to uncloak.
While enemy cloakers look the same as cloakers on your team, your alert status (Red, Yellow, or Green) can sometimes provide a clue as to who a cloaker might be. Your alert status is determined by the distance to the nearest enemy ship.
Phasers are your ship's primary weapons. You can fire once per second (faster if a starbase). The point-blank phaser damage depends on ship class: 100 for cruisers, 105 for battleships, 85 for destroyers, 80 for assault ships, 75 for scouts, and 120 for starbases. But the damage drops off linearly with distance. E.g. at that the same range that a cruiser phaser does 25 points, a destroyer phaser would only do 10 points. When a phaser hits a cloaked ship, the end of the phaser line segment shows the exact position of the ship (this is called "phaser lock").
When your ship has kills, you can beam up armies from a planet your team owns, if it has five or more armies. Planets produce armies (called popping) over time, randomly, usually 1-3 at a time. Each planet gets a chance to pop every forty seconds or so, on average. Normal planets pop 10% of the time when they get a chance, and pop 1-3 armies when they do, and get a 5% chance at a bonus army when they're below 4 to start with. Agricultural worlds have an additional 20% chance to pop 1 army, and also always pop one army when they start below 4. You can info a planet to see if it is agricultural. Planets also sometimes lose armies due to plagues.
To bomb an enemy planet, orbit it and press 'b' (once is enough). You can only bomb a planet that has five or more armies. Once you start bombing, the server gives your ship a chance to bomb every 0.5 seconds. Then you bomb 0 (50%), 1 (30%), 2 (10%), or 3 (10%) armies off. Assault ships bomb more at a time; they do 0 (50%), 2 (30%), 3 (10%), or 4 (10%). Beaming, by the way, goes at the rate of 1 army every 0.8 seconds.
Bombing and beaming require your shields to be down (they lower automatically when you start). You can fire weapons (if uncloaked), and det torps without interrupting bombing or beaming. You cannot beam and bomb at the same time. Raising shields stops the bombing or beaming process, as does entering repair mode. If you time it just right, you can raise shields just after beaming down an army, hit beam-down again before 0.8 seconds have elapsed, and not miss a beat.
Whenever you are near (almost overlapping) a hostile planet, it shoots at you invisibly. The rate of damage is steady, but is higher for each ten armies the planet has.
When you tractor a ship it pulls the ship towards you and you towards it, but without changing either ship's warp speed. The amount it moves depends on ship-type (mass and tractor strength), but not on distance. BB & SB have especially long-range tractor beams. Tractor beams cost 200 fuel per second. Tractor beams can pull a ship out of orbit, instantly stopping it from bombing, beaming, or fueling on it; that's why planet-takers usually cloak when beaming down. Tractor beams won't grab cloaked ships, but will stay on ships that enter cloak. (Note that if you have the visible tractor option on, it will appear as if your tractor beam is gone when your victim cloaks, but it isn't -- look for the T flag.) Pressor beams work the same way, only they push. Docking to a starbase interrupts tractor/pressor beams.
Your ship's engines heat up when you move and especially when you tractor or pressor. (The heating rate is one unit per warp speed per second, plus 5 unit per second that tractor/pressor beams are on. But your engines also cool constantly at 6 unit per second, 7 for a DD and 8 for a scout.) When the temperature is over 100, you have a 1 in 40 chance each tick (tenth of a second) of getting an engine burnout ("E-temping"), which leaves you at warp 1 for 10-25 seconds, and without tractors or pressors. (You can still steer and orbit though; and whether you can enter repair mode is unclear.) Similarly, your weapons heat up when you use them, and when your weapon temperature is over 100 they have a chance of burning out ("W-temp"), leaving you without weapons for 10-25 seconds. Detonating enemy torps also heats up weapons, and you can't det while W-temped. Weapon temperature is an especially important concern for starbases, although theirs can go up to 130 (150 on some servers).
Your ship constantly regenerates fuel, repairs its shields (and hull if shields are down), and cools its weapons and engines, whenever those operations are needed. These all happen at constant rates which depend on ship-type. E.g. if you're going warp 3 in a cruiser, your fuel tank will be filling up slowly because the movement isn't costing as much as your ship's natural regeneration rate.
SC, DD, and CA torps & phasers all cost 7 times their point-blank damage rate, in fuel. E.g. a CA phaser costs 700 fuel. AS, BB, and SB weapons cost somewhat more. Detonating enemy torpedos costs 100 each time you hit the key.
To get plasma torpedos, get two kills and refit to a DD, CA, or BB. Plasma torpedos fire out the front of your ship (except for starbase plasmas), track a little bit, and damage everyone nearby (even the firer) when they explode. They can be exploded by an enemy phaser (or on impact with a hostile ship or the wall).
To refit, you must be orbiting your homeworld or docked to your starbase, and have 75% shields, at least 75% fuel, at most 75% hull damage, and no armies. Refitting freezes your ship for 5 seconds. It's sometimes useful to refit to the same ship-type as you had before, e.g. to get plasma, or to bring your hull damage and engine temperature quickly to zero.
When your shields are up, damage you take knocks them down before hurting your hull. For some strange reason, the dashboard shows your shield integrity but your hull damage, so when you're getting hit the one decreases then the other increases. Hull damage reduces your maximum warp speed. Shields repair all the time, and hull damage repairs at half that rate but only when shields are down. You can enter repair mode to increase your repair rate (2x), especially when orbiting a friendly repair world (4x) or docked to a starbase (5x).
Rank and ratings do not affect the game at all, except that you need Commander rank or better to pilot a starbase on most servers.
Starbases can carry up to 25 armies regardless of their number kills. Also they come with short-range plasma they can fire in any direction. Starbases have 500 shields, 600 hull, and lots of fuel. But they only go warp 2, and cannot orbit foreign planets. A team can only have one starbase, and when it dies they must wait 30 minutes before getting another. A team needs to own at least 5 planets to bring in a starbase.
Some people have better net connections to the server than others, and this gives them a pronounced advantage in dogfighting (especially dodging and detting torpedos). Playing over a modem, you'll probably have comparatively bad lag, in the 100s of milliseconds. So you might have to lead your phasers a bit, because the ship your client displays will have moved by the time the server gets your phaser packet. "Packet loss" is an even more serious problem; your commands might fail to go through, and you might lose updates from the server. If you see motionless torpedos or other strange effects, you might want to request a full update with the = command. If you lose your net connection entirely, the server keeps your ship around for a while in case you come back, then destroys it (if no-one has destroyed your derelict ship), saying you were killed by "the Ghostbuster".
For course changes and firing of phasers and torpedos, the client (running on your computer) computes the direction from your ship (or where the client thinks your ship is, in lag conditions) to the location indicated by your mouse cursor, which may be on the tactical or the galactic map. It then sends this direction as a number 0-255, and the server decides what happens from there. For tractor and pressor beam engagement, the client finds the uncloaked ship nearest your cursor (in absolute distance, not direction), and tells the server you want to tractor (or pressor) that ship.
'w' brings up the war settings window. You can specify Hostile or Peace with each of the other three races, and then push Reprogram. You need to be at peace with a race to use the resources (e.g. fuel) of its planets, and also to avoid taking planetary fire damage while near them. You can even declare peace with your team's enemies and orbit their fuel worlds, but this will have two effects: (1) you won't be able to bomb or beam down on their planets, and (2) if one of them is at peace with your team, your phasers and torpedos won't hit him. If you reprogram a setting from Peace to Hostile, it will freeze your systems for 10 seconds. (There is also the War setting, which is what Hostile becomes after you hit an enemy, and disables resetting back to Peace until next time you die.)
Bonus trick for reading all of this: if you hold down the max-warp key while out of fuel, you'll fly pretty fast (e.g. between 8 and 9 for a scout) and cool your engines! (Discovered by Erik Lauer) Along similar lines, it's hard to tractor someone off a planet if he holds down the orbit key.