Instructions
Use an online map to locate one of the two co-op modes available in the game. Print out the map on a color printer for extra convenience.
Head to the icons in red for the two-player "Rampage" mode; both of you can now undertake a mission to complete a certain number of objectives --- for example, destroying 15 pedestrians while wielding a Micro SMG in under three minutes.
Travel to the icons in green for the "Free Roam" mode; both players can now do whatever they want in the game world, with the second player able to dress up in a variety of different costumes, such as that of a paramedic.
Activate the two-player mode by pressing the "X" button on the second player's controller when you arrive at one of the special icons in the game.