You just need to go to the option for playing a single game. I think the option is "Kick-Off" and then "Exhibition Match". Somewhere along the set up process (maybe the first screen) you will get a controller (side select) screen. This is where you can do what you need.
If you have two controllers connected, each control will be able to move to the left (home) or right (away) sides. If the controller remains in the middle channel it means it will not be used.
If both players move to the same side (and no controller is on the oppositions side). Then you will both play co-op against the AI.
If one of you moves to the left, and one to the right, then you will both play each other in a versus match.
You can also only choose to move one controller, which will result in single player against the AI.
You can play any number of players this way (2 vs 2, 3 vs 1, 4 vs AI etc.) up to the controller limit for the system you are using. I believe PS3 is up to 7, and XBOX is up to 4. I have no idea how the PC works with multiple players locally.
Pretty much the same applies in all other offline modes. In career mode for example, when you select to "Play Game" you will at some point get the same controller select screen. so you can move as many controllers as you want to your team. Depending on how you set up your career mode you may also be able to select the opposition side (i.e. play against a human rather than the AI).