I mainly just come here and post and ignore the trivial aspects of the forums, but what are the purpose of credits? How do they work with the donating and stuff?
You get credits for forum activity. Their main use is for vBetting. You can bet on any matches in the vBookie section, where there will be markets for almost all ATP matches during the year. You only win or lose credits, so it's strictly a game.
If you don't want to play this game you can donate your credits to someone else. Just press "Donate" under your credit total on the right hand of the screen, and enter recipient and amount (and a comment, if you want). Of course, you can't donate more than you have yourself.
You can also place credits in the vBank, which gives good interest (4% a month). That will give you more credits after some time. Ofc, that's only an interesting option if you feel you have use for them.