A good start would be to check the website and go from there. I don’t know of a good, singular guide unfortunately—there are a couple different ways of going about torrenting on I2P.
I can confirm that torrenting on I2P works quite well! You may have to set aside a couple weeks per movie, though. Still, the torrent selection is decent, if not quite as good as what you would get on the clearnet. You’ll want to check the postman tracker (tracker2.postman.i2p) once you have everything set up.