The rook
A rook moves in straight lines, as far as it likes, and jumps over nobody.
The rook moves in straight lines: along the file (up and down) and along the rank (sideways). As many squares as it likes, in a single move. What it never does is move diagonally.
These are all the squares this rook can reach in one move. Look at the shape: it is a cross. The whole d-file and the whole 4th rank, and nothing outside that.
Now there is a white pawn on d6. Look at what disappeared: the rook gets to d5 and stops. It jumps over nobody — not even its own. A piece in the way is a wall.
The pawn on d6 is black now. Capture it with the rook — in chess, capturing means going to the enemy piece's square and taking its place.
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