They look like a fairly bog standard advert exchange. They add your banner add to their database anrd give you some code to put on your web site. Every time someone visits your page then the code displays a banner from the add exchange's database.
Although these sites are popular with some web masters (as then can generate hits), users tend to dislike banner ads and some banner ad companies use their code snippets to trace users or place spyware on their computers.
As you can probably guess I'm not a big fan of banner add exchanges
I visit a web site for one reason only; it has stuff I want to read on it