PTC websites are based on
clicking add-sites and making their traffic bigger and bigger, by doing that you get 1 cent per click (depends on the account). So now the site gets clicks and you get cents. Sites that want to expand in traffic to their site pay money to PTC sites for advertising them (they pay ?$ for ?clicks) and a certain amount of that money goes to the PTC site founder and part of that money goes to clickers.
Most of PTC sites are based on referrals. That means that more of referrals you have more money you make so the more your referral clicks more money you get. For example: I get or buy 100 referrals, then i get 0.01$ from each click they made so if they wuld be at least 50% efficient that would mean they produce 500 clicks per day = 5$/day for me. And if you put all the numbers together you earn 150$ in one month.
And all of sites that are posted here actualy pay :)
Many of these sites require: