The acronym PvP means: Player-versus-Player. It is when 2 or more player-controlled characters fight. You can have a PvP fight 1-on-1 all the way up to 6-on-6. The first PvP map is free and comes with the game, but the rest you must either buy as part of a campaign or as a stand-alone map pack for some Platinum.You can create a password protected game so that only you and your friends can play, or not put in a password and make it open to the public.
However, PvP is not a very popular activity due to a lack of matches being hosted.