Basically, you can post your project on there with an amount you are willing to pay for a logo (or whatever graphic you want) designed. Then, bunch of designers design your logo and post it on there. you go back and pick on your like and pay for the service to that one designer.
I think that is a great idea because you have the ability to choose which logo you like the best. Here are my questions:
How much should I expect to pay for a logo?
have you ever used the site? What was your experience?