I want to buy a bunny and I do not know were to keep it my backyard has no grass?

A bunny does not stay in your back yard, if it is a pet , you will have it in a cage in your home, and take it out and let it run around the house.

If it is not a pet but for breeding, many are keep in out side coops ( if the weather is good enough) but these are pens off the ground, for the safety of the rabbit.