whaty is a bumpmap thigh do?

it will make your textures more 3D ish or stand out more

As far as I know, bumpmaps have been temporarily disabled. So, sell it or wait for a later update to be able to use it.

Bumpmaps work just look at nuthug

Bumpmap textures change the way light affects the given texture.
It often gives the texture a more realistic feeling.
The bumpmaps were said to work again in toribash 4.0.
If you plan on getting a refund for your bumpmap purchase, you won't.
Try selling the bumpmap on the forums, IRC, or ingame.
(Junibug: Nuthug isn't even wearing bumpmaps.)

I believe tertywerty is using bumpmap textures if you want to see an example.