It actually pays in proportion to the frequency and duration that you have the web site open. Here's a sample payout report that I posted in March. Right now, you have to use bitcoin to load the browser wallet. In the long term, it'll be a new token.
They're creating a new token so they can pay you for accepting the ad. It will be called BAT (Basic Attention Token) and built on top of Ethereum. The web site is here. The big drawback is that the only thing you can do with the BAT you get from them is to pay publishers. As I understand it, there will be no way for browser users to transfer funds out of the wallet.
That is a big drawback. If they want to grow they need to rethink that. Great info. Thank you.