Q4Max adds many features and fixes to Quake 4, making it a much more enjoyable and complete game. For this reason, most servers running Quake 4 are running Q4Max.
The Domination mode is a team-game where teams must attempt to capture and hold points on the map.
In this screenshot, you can see a player running towards a domination point to capture it - which will change it's colour, and start it scoring for his team.
Also notice the team overlay in the bottom right of the HUD - this is available in all team games, and allows players to see where their team-mates are in the map.