Trouble in Terrorist Town (TTT) revolves around a group of Terrorists (the players) who have traitors among them (referred to simply as "the traitors"). The traitors' goal is to eliminate all Terrorists who are not traitors. The loyal, innocent terrorists (the so-called "innocent") must of course prevent themselves from being murdered. However, the innocents do not know who is a traitor, and who is innocent...
The traitors are randomly selected at the start of the round from the group of active players. The number of traitors is a server-defined percentage of the total playercount (there is always at least one traitor). When the round starts, the traitors are notified and the game begins.
In order to beat the superior number of innocent players, traitors must use the fact that their identity is not known (yet). How they do so is up to them.
Once the number of players is large enough, Terrorist HQ will name a few innocent players as detectives, and supply them with special equipment similar to the traitor's special equipment. Additionally, whenever a detective searches a body, the results will be available to all players. Other innocent players should protect the detectives to maximize their advantages. Traitors will look to take out the detectives, because killing one gives a traitor more credits to buy equipment.
The traitors win when all innocent players are dead. The innocent win when all traitors are dead, or the time limit is reached with at least one innocent terrorist alive.
Individual players gain points by killing innocents when traitors, or traitors when innocent. Simply surviving the round is also worth points.
Teamkilling costs you a lot of points, and reduces your Karma. When playing as innocent, try to avoid immediately shooting everyone who looks remotely suspicious. You may well be gunning down someone from your own side, who might even save you later.
Every player has a Karma value. It starts at 1000, and goes down if you teamkill. At the start of a round, everyone who has a Karma below 1000 will have the damage they deal reduced by a certain percentage. As long as it's above 800 or so, the impact will be minor, but at 700 you'll already be doing only 80% of your full damage when you shoot someone. At around 500 Karma, it will be half.
Every time you damage someone who is on your side (e.g., innocent if you are innocent), your Karma is reduced by an amount based on your victim's Karma. So if you kill someone who plays carefully it will hurt your Karma more than if you shoot a teamkiller. You can see other player's Karma as it was at the start of the round on the scoreboard, and on a description when you aim at them, which goes from "Reputable" (green) to "Liability" (red).
During a round, Karma is updated behind the scenes. As soon as you damage someone your Karma goes down. So if you are Innocent, and you see someone kill multiple other innocents, you can safely shoot him: he is either a traitor, or a teamkiller who will have low Karma.
The updated Karma is not displayed on the scoreboard and crosshair info, because that would let you easily figure out if someone is a Traitor. This is the difference between Base Karma (shown on scoreboard etc) and Live Karma (updated "live" during a round). After the end of the round, your Live Karma becomes your Base Karma, and you can see everyone's up-to-date Karma on the scoreboard.
At the end of each round, you regain Karma if you are below the maximum. If you did not damage a teammate that round, you will receive a significant bonus.
In general, your Karma will be okay as long as you don't consistently kill teammates every round.
Each round has three phases: preparing, active, and complete.
In the preparation phase, all players spawn and can start gathering weapons, exploring the map and getting into position.
When the round starts (and enters the active phase), the traitors are selected and notified. The round timer starts ticking down and the traitors have to start their dirty business.
As soon as either party has won, a victory screen is shown and the round complete phase starts. In this short phase everyone gets a chance to look through the victory screen. When the time is up, a new round starts with a new preparation phase.
Many servers run the gamemode in detective mode (it is enabled by default). This means when someone dies, you will not see it immediately on the scoreboard or in a death notice. Instead someone must find the body and search it (using the Use key, default "E") to identify it.
Once a dead player's body has been identified, he will no longer show as living Terrorist on the scoreboard, but will be shown as "Confirmed Dead".
Dead players and other spectators can also see players who are "Missing In Action", meaning they are dead but their body has not been identified yet. Note that innocent players do not have this information.
Servers that do not run in detective mode will show dead players as being on the Spectator team as soon as they die.
As a spectator, you cannot communicate with the living players if a round is active. This prevents spectators from revealing the traitors, and other game-spoiling information.
If you are a spectator, only other spectators will hear your voice chat. You can text chat with fellow spectators by using the team chat key.
As a living player, everyone will hear your voice chat. If you are a traitor, you can use the Sprint key (default "Shift") to send your voicechat only to other traitors.
Traitors have the ability to buy special equipment from a selection of useful items and weapons. This costs a credit, and you usually get only one at the start of a round (you may get more as a reward for doing well). If a traitor carrying a special weapon dies, it will drop just like his other weapons, and can be picked up by anyone. However, you can only carry a single special weapon at any time, just like other weapon types. Hence, if you already have C4 in your inventory, you cannot also pickup a silenced pistol that someone dropped. Items do not count towards this limit, so you can for example have Body Armor, a Radar, and C4.
If you are a traitor, press the "Context Menu" key (default is "C") to open the equipment screen. Select your choice and confirm it to receive the equipment.
The following keys perform a special function in TTT:
Pressing the key that Suit Zoom is set to in your keyboard configuration will show a little popup with voice commands. Pressing the number key listed for a voice command will send the text to the chat. For some commands this will include the name of the player you are aiming at.
You may want to bind certain voice commands to dedicated keys, especially if you don't have a microphone and find you can't type quickly enough in sticky situations. I assume you know how to bind a key that isn't in the keyboard menu. If not either google on something like "bind key Source" or ask people.
The console command used to send a quickchat is "ttt_radio". You need to supply which quickchat text to send by adding its name, for example: "ttt_radio help" to send the "Help!" chat. Binding that to a key could look like:
bind "h" "ttt_radio help"
Entered into the console of course. These are the possible quickchat names: