They send you some via the internet some work units, your computer while it is idle or not playing games starts crunching numbers for them. Once the work is finished boinc sends it back to them for evaluating if anything significant comes up.
There are millions of people who use their computers across the world to crunch numbers, rather than spend enormous amount of money on faster systems, which normally would cost them squillions of dollars/pounds/euro to do so, the whole concept of boinc is to send it to the people who signed up to do so, perfectly voluntary...how do I know? I used to be part of seti@home, until I decided I can't do this no longer, since I didn't have a proper internet.
If anything significant is found, like they have found E.T. they might tell you, depending if it is a threat to national (mainly America) security
