You've probably seen a lot of things like this over the sheets you've browsed. You're looking at an online shop, looking for a watch but you get a flag that advertises a gondola.
While you might, at some later point want to buy a gondola, right now you're looking for a watch and it would have surely been nice if the banner were advertising a watch because then you would have probably clicked it.
Well, that's also what the kinfolks at Google thought of, so they came up with an assassin idea. This is known as Google AdSense, and it's known as a targeted publicizing platform
What you do( as a web decorator/ website owner) is, instead of startle through hoops to get some flag on your area that your guests won't even care about, are you simply allocate some part of the screen.
You then sign up for the Google AdSense program, you put a small snippet of code in your webpage and Google ensures that in the place you specify, a banner will be presented, presenting adds relevant to the contents of your area.