Pawn
A pawn moves straight forward, captures one square diagonally forward, and never moves backward.
A pawn may advance two squares from its starting rank if both squares are empty. Reaching the farthest rank requires promotion.
Pawn moves and captures are different
A pawn advances straight into an empty square but captures one square diagonally forward. From its starting rank it may advance two squares when both squares are empty.
Move the d2-pawn forward or capture one of the pawns on c3 and e3.
Move the d2-pawn forward or capture one of the pawns on c3 and e3.
Pawns do not move backward
White pawns move toward rank 8, while Black pawns move toward rank 1. Once a pawn advances, it cannot return to defend a square it left behind. Pawn moves therefore change the position more permanently than most piece moves.
Two special rules apply only to pawns
A pawn that reaches the last rank must promote. A pawn may also be captured en passant immediately after making a two-square first move past an enemy pawn's capture square.