Hit the space key to draw Click the thing up at the top to switch between circles, squares, the line tool and the square tool. (More shapes are coming soon) Click the arrows the show the sliders that allow you to adjust the color of the outline and fill. Press and hold the space bar when the line tool is selected. When you release it it will draw a straight line between the 2 points. Press and hold the space bar when the square tool is selected. When you release it it will draw a square between the 2 points. If you want to erase set brightness to 100.
If it isn't showing up than check that the size is not 0 and that the saturation is not 0. The Square tool is buggy if you move your mouse fast. Please comment what I should add next.
