I love my two Holgas. To learn more and make some slight modifications to eliminate light leaks (unless you like that with a holga) and cut out the film insert to hold the film flat in sq format here is a good sight:
I use Arista 400 and soup it in Rodinal. I have modified one holga with a larger aperature and recalculated depth of field for the new F-stop. I had a third that I had removed the spring and locked the shutter open for night shots but broke it.