Users download and install a client program which runs on their computer when it's idle. When the program finishes a small "work unit" the results are returned to the FAH servers. So far, almost 500,000 users have donated processing time for almost 1.4 million CPUs, far more computing power than the largest supercomputer.
If your computer sits idle a lot, you should consider running FAH, as this is a huge benefit to scientific understanding which will certainly lead to cures for major diseases.
You can get more information about FAH and protein folding here: http://folding.stanford.edu/