Drag the applier to use it. You will only be able to draw with it when the cross is a tick. Convert the cross to a tick by clicking on it. You can turn it back to a cross by clicking on it again. Drag the applier to the polish bottles to change the colour. Click the nail polish remover bottle to clear all the nail polish. Drag the bracelets to the hand. Click on any of the nail stickers and you will get one which follows your mouse pointer. Click to place the sticker. You can do this as many times as you want with one sticker, press space to delete the usable sticker. Click the background to change the skin colour.
If you have any suggestions for things to add, comment them in the comments.
