How does it work?
First of all you have to register on any of those companies(listed above) and then at the dashboard you have to shorten the long url(which you want to share) through their service. now start posting those short url in forums, blog, mail etc. When the visitor(or receiver) click lon those links, you make money from a redirect that can be an interstitial, pop up or top frame type advertisement.
It is one of the easiest form of make money online.