By default (you can turn this behavior off if you wish,) Brave will periodically (every 120 minutes or so) popup an ad. The ad doesn't appear 'in the browser window.' On Windows 10, for instance, it pops up in desktop Notifications. The ad is a sentence of text and a button, full stop. No video, audio, animations, or anything creepy. Just a little dialog box you can click or dismiss.
Every time that happens you receive BAT, a cryptocurrency, that accumulates in your automatically created BAT account. You do with it what you will but, by default, it is periodically distributed to sites that opt-in to accepting BAT.
You have to "activate" the notification to open the resulting page, or you don't get paid. But it's a quick click and close. Honestly once or twice I've actually looked at the site a bit.
