How do you play multiplayer on battlefield 3

Depends on Ps3 Xbox or PC for all of them you have to have some type of internet connection, wireless, wired, for Xbox you have to have Xbox live which is 15$ a month or a year I don't remember for Ps3 and PC its free, when you start the game you just select multiplayer from the main menu and pick server to play on, join it, and you are all done.