Classifieds Pay Questions


I am just having a look at the classifieds plugin. I see that you can set up a credits pay system, but I don't know where members pay for credits. I am using a single install of wp with bp. If you choose credits, does that mean you don't use checkout? In the checkout it has annual and one time payments. Is annual for one ad or as many as you like for one year? And what is one time, is it an ad for a week? Is this related to the credits because I read that you can buy credits in packs of 5 or 10, but I haven't seen this.
Sorry I know these are basic questions I did look for the answers, but couldn't find them.

Also it says that uploading an image is optional, but for me it is required, how could I make it optional?

Thanks so much.