Chess rules
Pawn promotion explained
A pawn that reaches the farthest rank must become a queen, rook, bishop or knight.
When promotion happens
White promotes on rank eight and Black promotes on rank one. Promotion is part of the pawn move and happens even when the pawn captures on the final rank.
The new piece appears immediately. The choice is not limited by pieces already on the board, so a player may have two queens or more.
Queen or underpromotion?
A queen is normally best because it has the greatest mobility. Choosing a rook, bishop or knight is called underpromotion.
Knight promotion can give a unique check or avoid stalemate. Rook or bishop promotion is rare, but may be correct when a queen would produce an unwanted draw. Wizard Chess pauses the move so you can choose.