It will upload by itself and get you new work to work on too as long as you are connected to the internet. Once they receive your work unit they (their computers or whatnot, I don't know the details) will process it and allocate you credit for having done it. Credits are really just to know how much work you've done (especially compared to others who are working on the project). You don't trade them in for anything and they don't have any really value but it's always fun to see the numbers go up.