The Pawns - basics
The pawn is now able to travel up to 4 squares in one go on its opening move. The pawn on b2 enters the empty field b5/6 and can choose to occupy either square.
Similarly the pawn on g12 is entering an empty field and can choose which square to occupy.
The pawn on e7 has no option other than to move one square to e8.
See en passant