The bishop moves diagonally, as many squares as you like, but never straight up, down, or sideways. Because of this it always stays on squares of the same colour it started on. A bishop on a light square can never reach a dark square.
In these puzzles you take the bishop to the goal square around wall pawns. Every goal is on the bishop's colour, so it is always possible, but the walls will make you zigzag.
Tip: trace the diagonals from the goal square backwards. Where they cross a diagonal your bishop can reach is where you need to land.