Uh, how do speakers work?

[jedusor]

I just scored a stereo (two-cassette, five-disc tray) with a subwoofer and two tower speakers off Craigslist Free Stuff. It's gorgeous, and it seems to work fine--all the appropriate lights turn on, and I can hear the music really faintly when I play a CD. I just have to find the appropriate cables to plug the speakers in. The backs of the speakers look like this. What do I need? I've never put together one of these setups before.