To use eraser, hold down over eraser and drag over art, when you release it will be back to brush and ink. Circles and square stamps can help with shapes, but since there are no layers, you'll see it still, or have to erase it. click brush to reset. change ink Brightness, Pen Color, and Pen Size as needed.
@_TheNightRaven Take screenshot. (Change ink brightness to make it white, black, gray, and try adding lighting! {challenge! use this as a replacement of your art app/website just for three projects, and the send me the links so I can see how it went.}) Better to change canvas color before erasing or drawing.