Eraser tool erases, Brushes paint.
Click on the different brushes to paint.
You can't erase with the differently styled brushes, but there is a single brush for eraser.
I think I may have come up with a work around tho....
You can paint with any of the paintbrush tools, then use the eraser tool to flood the color with "erased" pixels.
There are some caveats, but it works pretty well for me.