Nowadays, it supports many different videogames: DotA, Warcraft 3 : The Frozen Throne, Call of Duty 6 : Modern Warfare 2, Left4Dead 2, Call of Duty 4: Modern Warfare, Call of Duty 5: World at War, Left4Dead, Killing Floor, Red Alert 3, Counter Strike 1.6, Counter Strike: Source, Starcraft, Call of Duty 2, Borderlands, Battlefield 2, Enemy Territory, H.A.W.X, TrackMania, Age of Empires 1: The Rise of Rome, Age of Empires 2: The Conquerors, Dawn of War and Quake 4.
You have to install the videogame you want to play online and then, run Garena to associate them.
Once they are associated, you only have to play the game and enter a game room in Garena.
Garena can be really interesting, because new games usually offer interesting online capacities which are powered up thanks to Garena.
Trial version doesn't grant you priority in queues.