The term PTC means paid to click. A PTC site is an online service where you get paid to Click. On such a site different advertisements will be shown. You have to be a member of that site simply free. Then you have to click and watch the ads for some seconds. After the time frame is over (usually around 10 to 30 seconds) you get paid. Not much, only some cents for each ad, but it adds up the more ads you click, especially on a daily basis. Most times you can also earn from members you have referred to a PTC site.
Imagine the income potential with so many referrals...!