First, you need to make sure the "Layers: Face/White" button is selected (it's the one in the upper left corner).
To do the face, then just select the character you are making.
To do the white part, SHIFT then the character you are making.
If you want to do the Outfit/Tongue, make sure the "Layers: Outfit/Tongue" button is selected.
Then for the outfit, just select the character you are making.
To do the tongue, SHIFT then the character you are making.
Same thing for the Layers: Shoes/Ribbon/Hat. Select the button on the left, and then the character or SHIFT then the character.