The audio output jack on the computer (green) takes a 1/8-inch stereo plug, also called a mini-stereo plug. On the Bose rear panel, the audio inputs are red and white RCA jacks. So you need an adapter cable with suitable plugs on each end. Radio Shack sells a couple of them in different lengths. Here's a link to one of them
so you can see what it looks like.
All you need to do is plug in the cable at each end, select the rear audio input source on your Bose, and you're in business. Make sure you have the computer volume set to its full level in the Windows sound settings so you'll get the best performance.
If you need a copy of the Bose owner's manual for reference, you can find it here at Bose