Your best bet would be to do a google search since such a response to your open question would fill 20 pages.
What audio program are you using? You may need logic pro or digital performer to do basic 5.1 mixing.
If you're trying to figure out the artistic aspect of mixing, try loading up a few Hollywood DVDs and extracting the 5.1 ac3 files. Use an audio utility to decode them into aiff files and play back each channel in your video editing program to see how its mixed. That'll give you a basic understanding of a professional 5.1 mix.