"Folding@home is a distributed computing project -- people from throughout the world download and run software to band together to make one of the largest supercomputers in the world. Every computer takes the project closer to our goals. Folding@home uses novel computational methods coupled to distributed computing, to simulate problems millions of times more challenging than previously achieved."
This project is allowing biologists to fold proteins. I am no biology expert, but in English, it will help to eliminate some diseases.
EDIT: In comments, some people do not understand what this program does. It uses your computer to help them fold proteins rather than having to buy new computers to do the same thing. This helps them because they might buy 3 computers to help them at their end, but people allow them to use their computer to do calculations. This adds more computers to the project.
Step 1: Download the Client
Step 2: Installing the Client
When it finishes installing, uncheck the "View ReadMe" and then click finish.
Step 3: Use the Program
Step 4: Let the Program Run.
Step 5: Changing Your Username and Team Number
Edit: I created a team, as suggested in comments. The team number (what you enter) is 129004. Make sure to not have the period.