The Dance Floor is a type of furniture, but a special one. It is used to breed bunnies, by placing two bunnies on the Dance Floor. They both must be at least level 4 to breed. Once that's done, it will show you a menu of possible offspring you can have. You can choose two kinds of music. The breeding time is different for each Bunny. The longer, the better because you can even get a valuable, rare bunny. Once you reach level 15, you can buy another one.
For a list of breeding combinations, look at Breeding Guide.