Hello guys i know im in the wrong segment but is the sandpaper buggy or is my IQ to low to use it ?

Normally you place it on your left hand and maintain right-click with the item you want to 'grind' in the other hand

Please follow the "Feedback and Help" link on the project page if you have questions about the mod.
Maybe the in-game tooltip can also help you figure out how to use the item. Cheers!