porn tubes are monetized by ads. usually ads for dating sites. sometimes dick pills or sex toys, too.
you don't build an affiliate network, you join one. they give you a link/banner to put on your site. this is your "ad".
you then promote your site to get traffic [visitors] and a percentage will click your ad. a percentage of those will sign up and you will gain revenue.
popular networks are chaturbate.com/affliiates and crakrevenue. you can also search "Dating" "adult" or "male enhancement" on offervault.com and find more networks/offers.
but if you're thinking about building an affiliate network, i agree with
@bendutchman you're in over your head