Perhaps you do not know about the en passant capture rule?
how do pawns make a diagonal move when sitting adjacent to each other
Hi mango920--you're likely talking about en passant, which can be Googled if the following doesn't make sense. When one player has a pawn on his 5th rank (so that would be a5-h5 for white and a4-h4 for black) an enemy pawn moving two squares on its first turn will land on the same row. If these pawns are next to each other, the side who didn't just move can now capture the pawn as though it only moved one square. So a white pawn on e5 can capture a black pawn on f5 as if it had only moved to f6. This must be done after a 2-square advance though, it must be on an adjacent file, and if it does not happen on the immediate following turn then the opportunity is lost for the remainder of the game.
how can pawns make a diagonal move