Press start, then click to draw the sprite color. Press space to scroll through the shapes-erasers. Then use the scroll wheel or up/down arrows to change color, then use left/right arrows to change brightness, then use w and s to change transparency. Click space to hide the graph or r to show it.
You can make something and take a screenshot and that can be used as a sprite if you want (just add credit.) I used one script from one of my old projects. Once you draw something please take a screenshot and make a remix and upload it as a background if you want.