I am assuming these are just standard speakers with only connections for speaker cable. In that case, you need some sort of receiver/amplifier to power the speakers and translate the speaker cable connection to something your computer understands (most likely a mini-stereo connector or if you are lucky a digital audio connection)

I have a small bookshelf style stereo which I connect to my PC via a Y stereo RCA -> 1/8 stereo cable. I think this a very typical way to connect PCs to sound via an analog connection.

I don't really see a way to go directly from speaker cable to your computer.