It’s basically a software you install to donate your computer’s idle power (ie typicallywhen the CPU does nothing) to help scientists with the huge amount of calculations that simulating the folding of protein requires and that not even the best supercomputers can achieve alone in a reasonable time. It’s distributed science. I’ll admit I still don’t grasp what folding means in the context of proteins. The programme folding@home started around 2000 and is still running ie you can still donate CPU time today