doubt about pawn

You might be referring to "en passant". That's a special sort of capture that only a Pawn can make, and only under certain conditions.

If the opponent has a Pawn still sitting on its home square (on d7, for example) and he moves it two squares forward, you can capture it with your own Pawn just as if the enemy Pawn had moved only one square forward instead. In order to do this, your own Pawn would need to be on your fifth rank:

Googling how a pawn can cut another pawn and still confused.🤔

Next doubt, three fold repetition.

How about the one where your opponent appears to cheat by moving two pieces, the king and rook?

omg

I also hate the one where they think you aren't looking and they take a queen off the board and put it where a pawn is on their 8th rank. They move the pawn off the board, why? Why don't they just put the queen on an empty square?