New to Gaming, Controllers....

Hai. I was recently given a PC by one of my colleagues, I've never played PC games before, I was advised to get hold of Battlefield 3 because of the intense multi player modes. The thing is, how the hell do you play it using a usb Snes pad? As I understand it most pc games use a keyboard and mouse, but this seems silly if you already have a controller available. Has anyone else had this issue playing Battlefield 3?