Each one is different but it comes down to ads, subscriptions/memberships, and taking a cut from revenue by original creators. They can also make money from production companies promoting their materials on the site, which is a form of advertising but not just banners/pre-rolls.
Well firstly you need the right physical attributes as a male or female talent or at least have an interested audience for your content .
I am not posting link here for obvious reasons but on their site they clearly detail 6 ways you make money from video uploads and the split you get etc. You can search "earnings and payouts" on their site.
Whats interesting is they payout via Cosmopayment which means you get an ATM card to take earnings out.
It's easy for them to make money. Actually people ripp off other adult webmasters content, edit the videos and reupload them again. So the more fews the more money.
Some may make good money while most will get their content taken off because of copyright infringements.