They are for the casino mainly (top right under games). You can invest them or donate them. You get them for posting, logging on, and participating in polls or answering one of jsteinb95 's questions.
You are not alone with your quest lol. These links may help, the stock market section is currently unavailable so disregard that part for the time being.
haha cool! so i can go from just looking around the web for random stuff to getting addicted to FZ6 gambling!!! great job mods! haha...this is kinda a cool thing to put on a forum...makes for more fun...and i really just posted this to get my 20 credits lol
I'd like to take this opportunity to apologize to the many Forumites who have donated points, thank yous, fake dollars, rep powers, MQ's, QR's, and used clothing to me; I haven't a clue how to use any of it so they just sit there. I'm sorry!