Click the green flag to begin. Use the sliding scale to select the size of your drawing pen. Choose a color from the color palette at the bottom of the stage. Click the color you want and then click/drag to begin drawing. Click ERASE to erase your drawing. Have fun creating with the Scratch Pen extension.
Thanks to SL Smart Mind for the Scratch Tutorial | How to make a Painting Game in Scratch 3.0| Scratch Extension | Scratch 3.0