I went on some of the popular ones, but don’t really understand what they are. Do you just post any website, article etc, and that’s it. Does it cost money??

One of my referal code is www.xyz.com/?referid=4567 . That means anybdy who clicks or types tht link in his browser, i get paid. Now my question is CAN I USE THE TRAFFIC EXCHANGE AND INSERT THE SAME PARTICULAR LINK CODE SO THT OTHER CLICKS THT PARTICULAR LINK. If yes, thn is it so much eazy 2 earn money online? Plz internet marketers only answer. Understand my question properly, m saying th same particular link 2 b clickd by othrs in xchange 4 their link (whch i wil click ofcource), m nt saying click on any banner or anythng, T H E S A M E P A R T I C U L A R : X A C T L I N K. If yes, thn can i do th same wit social bookmarking sites also?

I can understand that some free sites make money from ads. But how do sites like Reddit and StumbleUpon make money?