A PTC site (Paid to Click) is a site that pays you to view websites linked from their page. They  also pay you for people you refer to their site . You won't get rich, but you can make a steady income if you stay with it and get referrals.. 
You can also pay to have your site advertised.

For Example:
» You click 10 ads per day = $0.1
» 20 referrals click 10 ads per day = $0.5
» Your daily earnings = $0.6
» Your weekly earnings = $4.2
» Your monthly earnings = $18

It doesn't seem like much, but if you do 4 to 6 sites a day, it all adds up!