Operating out of the shotgun, and generally utilizing a man in motion to force the defense to respect the outside threat, a Wildcat "quarterback", after having a moment to process the defense, has the option of handing the ball to the man in motion as he passes, running the ball himself, or throwing a pass. All this action and the variety of potential weapons make it tough on a defense to defend.
Along with confusing opponents, the rotation of personnel creates an 11-on-11 attack in the running game instead of the 10-on-11 situation usually presented when a quarterback becomes uninvolved in the play once he hands the ball to the running back.
In the rotation of players, sometimes the quarterback is split out to a wide receiver position while a running back lines up behind center. Other times the quarterback is taken out of the game completely and replaced by a player who specializes as a Wildcat quarterback. Some teams like to add an extra offensive lineman to create an unbalanced line as well.
There are many variations of the Wildcat offense currently being run in the NFL.