The goal of CopyCat is to copy the given image for each level onto the canvass.
Drag stencils from the right panel to the left canvas, then click a glob of paint. Paint will go everywhere on the canvas except where you've placed stencils.
Colors mix as you'd expect them to, but if you need a reminder, click on the 'Help' note near the stencils.
To get rid of a stencil, drag it to the trash can. To remove all stencils, click on the trash can.
White paint covers over any color.
Be creative, sometimes you need to use a series of different stencils to paint one weird shape.