Re: Using Paypal
I'm not sure if you're asking this as a pre-sales question (as in, you haven't purchased CP yet), or if you have purchased, and can't figure it out? So, I'll answer as if you haven't yet purchased CP..
Within your
WP Dashboard, ClassiPress settings > Payments screen, you can set up your payment and pricing options for the ads on your site. Assuming the example you're asking for is to charge for all ads, you would set the Pricing Structure to "Fixed Price Per Ad" and also set the price per ad.
From the user aspect of it, when they click "Post a Classified" and complete the fields, once they submit there will be a paypal button and message that the ad will not appear until they have paid. You may want to look at the demo site for what this looks like. CP Demo
http://wpclassipress.com/demo/.
I hope I have understood what you're asking and that this clarifies it for you