You may already know the Butano doc: https://gvaliente.github.io/butano/index.html
Butano comes with very useful examples as well. You might want to check the "Map Collision" one. https://gvaliente.github.io/butano/examples.html
If you still have questions, you can ask in the gbadev Discord, there's a #butano thread. https://gbadev.net/
Good luck!