Naming the fingers on the piano is very simple to do. It’s one of the first things you will learn in your piano lessons. Just like the hands are mirror images of one another, so are the numbers used to name them. The thumbs are given the number 1; the index fingers given 2; the middle fingers given 3; the ring fingers given 4; and the pinky fingers given 5.
When you read piano scores, you will notice numbers written next to the notes. These numbers correspond to the fingers of each hand. On the piano, the right hand typically plays the upper staff, and the left hand plays the lower staff. Since the hands play separate staves, it is easy to tell when the number 3 corresponds to the left hand or the right hand.
However, sometimes the hands can play on different staves. To avoid confusion with fingerings and reading, it is common practice to mark notes played with the right hand on the lower staff with RH and left hand notes notated on the upper staff with LH so that this eliminates any chance of confusion. You may also see the right hand abbreviated as m. d. (main droit in French, or mano destra in Italian) and the left with m. g. (main gauche in French) or m. s. (mano sinestra in Italian).