The pawn
Forward only
One square straight ahead. From its starting square, one or two.
Capturing
A pawn captures one square diagonally forward. A piece straight in front blocks it.
Promotion
On the far rank a pawn becomes a queen, rook, bishop or knight. Almost always a queen.
Pawns never move backwards or sideways. Black's pawns move down the board, towards rank 1.
Promotion is why a pawn near the far rank is so dangerous. There is one more pawn move, en passant, in Unit 2.