It is similar like a commercial referral scheme. Example, if you refer your friend to a local bank, then your bank would give you some sort of incentive or a gift for doing so.
In affiliate marketing, it is abit different because instead of referring your friend, you refer online visitors to a selection of different product/service offerings. In return, you will be then rewarded with large amounts of commisions.
Carefully study the picture below.

If you agreed to participate in an affiliate program only because the commission rate was high and you don’t know a bloody thing about the product you’re selling, you might want to rethink your choice as the chances of you failing it is quite high.
While niche marketing may sound a bit odd on the surface, it really is the way to go. Making your site focused and concentrating your energy on a particular group will make it seem more legitimate and you can count on better business in no time flat.