There are varying different game-modes in Team Fortress 2, each with their own set of rules and maps. There is Capture the Flag, Control Point, and Territorial Control.
Capture the FlagEdit
The goal of this game-mode is to steal the other team's secret intelligence from their base and bring it back to your own base. The intelligence is stored in a briefcase, located deep within each team's base. If a player is killed while carrying the briefcase, it will drop to the ground and a timer starts. The team that the briefcase belongs to cannot pick up the briefcase or return it to their base, but players from the opposing team can still pick it up and continue their theft attempt. If no one mamages to grab the briefcase and the timer runs out, the briefcase will be returned to its home base.
See also: Capture the Flag
Every Control Point map is a little different, but the main goal is to capture and hold all of the points in the map. In some cases, the Control Point must be captured in a particular order - the points are displayed at the bottom on the HUD in the team color pf the current owner. If there is a lock on the point, then it can't be captured.
You capture a point by standing on it. The more players that stand on a point, the faster it is captured. Th eopposing team can "block" a capture by standing on the point at the ame time as the capturing team. Ownership of a point stays with the defending team until it is fully captured. If the capturing players are defeated before fully capturing the point, the capture progress will gradually decline unless new players from the attacking team reach the point and continue the capture.
In Territorial Control the goal is to take over the entire map by capturing 'territories'. Each game is randomly selected from the six available layouts in a 'point against point' game where both teams must capture the opposite point while defending their own. After a team successfully captures the opposite point, the next round takes place in a different area of the map which is also randomly selected. After a team captures all four territories, that team must capture the enemy team's base. If the base point is captured (in Hydro, the Radar Dish for RED, The Power plant for BLU), the attacking team wins the game. When the next round begins, territories are reset and a new random layout is selected.