PvP stands for Player vs. Player. This means attack actions taken against another player.

In order to attack someone first go to that player's profile page and then press "Fight" button underneath their stats window.

After that you will have an option to choose how to attack them.

Fight - Takes energy and cash from your opponent
Dance Off - Takes energy and cash from your opponent
Prank - Takes more energy from opponent
Eavesdrop - Can learn information about your opponent and how they've built their account

Fights scale based on your Strength.
Dance offs, pranks, and eavesdrops scaled based on your Intelligence.

You can read more details about how PVP work's in the forums here!

Have fun PVPing, but remember not to be a jerk!