is it any sticker or a specific one?
ok i think i misunderstood, so if you are asking how to get pass the level as in the second screenshot... you got the body anatomy sticker right? then you drag the fire sticker onto it, and the two stickers turn into a single key. then when the man in the background appears, you drag the key onto him, and you will get a different key with two holes in it. click on both holes.