Basically I usually turn on my desktop PC, go and do something else whilst it's booting up, maybe go on the internet and check my emails and generally surf a bit, and then I may actually do some work on it (usually photoshop and dreamweaver).
Now there are large gaps when I'm only using a fraction of my processing power and this is where I can do my bit in helping humanity.
I install a small program (I'll spell it this way as they are a US company) and this downloads calculations for my PC to ...um... calculate. Currently the institute is working on the role of proteins in the body -'Human Proteome Folding Project.'
Small encrypted files of protein data are sent to my PC when I am on the net, and then I don't need to be on the net for the magic to happen, and when I do get on the net then it sends back the results.
Currently there are thousands of users linking into this Grid, and it has been estimated that 4,000 years worth of computer calculations have been done in the last 3 months!
People like recognition for when they do something charitable so there is also a ranking system where your run-time and calculations add to your total points.
If you'd like to help to then visit the World Community Grid