The Pirc Defense is a hypermodern defense, meaning that it doesn’t try to control the center early on with his pawns. Instead black tries to attack the center with this minor pieces from the sides and then once the foundation is in place, then looks to undermine the center control that white usually has.
There are two main attacks that white has to play against the Pirc Defense. The Austrian Attack is the most aggressive as white pushes his f pawn to f4, exposing a weakness on his king side but putting added pressure on the king side of black. It is usually a good idea to aggressively attack a king that is castled on the side of a fianchettoed bishop which black does in the Pirc defense with the moves g6 followed by Bg7.
The second move that white has is the Classical System which develops the second knight to f3 and looks to build up a stronger center control before white looks to attack.
In both cases, black will have counterplay but has to be cautious about playing to passive. If black is not careful he can find himself in lots of danger and a position that is too cramped to move. Black will have great play if he attacks the center for white before white has a chance to attack.
Watch the video below to get a detailed explanation of the Pirc Defense.