There are two teams in Counter-Strike, the terrorists and the Counter-terrorist.  The terrorist are the one who blow things up, take hostages, assassinate presidents, etc.  The counter-terrorists are the ones who try to stop them. 

     When you join a game you first choose a team and then you choose your character or player model.  Each team has five different player models to choose from, and these player models are really nothing more than how other players see you.

These are the terrorist  

These are the counter-terrorists

     What's great about CS is that all of these characters have the same "skill" level.  This means that no one character is any powerful then the other.  Every character has access to the all the weapons available to the rest of his team mates.