Basically you download a program and it runs in the background using the computer cycles that you aren't actively using.
I have a CB team (3 members currently) and we are ranked 5683 of 35542...we can do better than THAT! So if you want to join and/or want more information, go to http://folding.stanford.edu, sign up, and help us out! The team ID is 41446. Thanks... now fold those proteins!