Place the numbered stickers on the appropriate piano keys as instructed by the sheet music. Usually the stickers are numbered 1 to 12, with 1 going on middle C (C4) and 12 going on G above high C (G5). Place the stickers on the white keys only.
Look at the sheet music, playing the keys indicated by the numbers on the sheet. For example, if you see the number "3" three times, it means to strike the key labeled "3" (usually E above middle C, or E4) three times in a row. Rests are indicated by asterisks, and measures are shown by vertical lines. (Most simple songs should be in 4/4 or 3/4 time.)
Remove the stickers from the piano when it is time to progress to standard music notation; they are designed to not leave a residue on plastic or ivory keys.