Promotion

If your pawn reaches the far rank, it does not stay a pawn: it transforms. You choose into what — queen, rook, bishop or knight.

Almost always you choose the queen, because she is the strongest. You may have two queens, or three: nothing forbids it.

Once in a while a knight is better than a queen — because only the knight gives a check the queen could not. It is rare, and it is lovely.