Look at the pictures under "Delétang's triangle method"
https://en.wikipedia.org/wiki/Bishop_and_knight_checkmate#Del%C3%A9tang's_triangle_method
Look at the pictures under "Delétang's triangle method"
https://en.wikipedia.org/wiki/Bishop_and_knight_checkmate#Del%C3%A9tang's_triangle_method
What piece of advice made it easier for you to understand how perform the mating pattern?