Try to use the marker at size 10 or higher so it fills in completely and doesn't leave gaps. (Right-handed controls) Y switches between your current tool and the eraser, and B brings up the color dropper. Right on the d-pad brings up your tool selection. L is undo, R is redo. Up/down zoom. Using the smudge stick at 50 opacity or lower makes it smoother and easier to use without making mistakes.