Pintbrush tool

I was wondering if anyone knows how to make the paintbrush tool cut. By this i mean is there a way to make the paintbrush tool get rid of the background instead of colouring it white, so that when i paste an image as a new layer on top of another layer, the white does not show over the top of the bottom layer.

Select the "eraser" tool, and in the eraser tool "options" pallet change it to act as a paintbrush. It by default will be set to "Block"... open that dropdown menu and select paintbrush