I haven't bagged before, but have done some reading.
Release film, usually mylar, is used to prevent the skin from sticking to the vacuum bag. Often you lay out your glass and resin on the release film before applying it to the core (film side out, of course).
Breather layer is a section of porous cloth used to allow the air to travel out of the bag through the vacuum port (where you attach the vacuum source). If you don't do this, the bag can get sealed around the vacuum port, preventing the uniform removal of air from the bag.

What is it you're trying to accomplish? Make a stand-alone skin replicating your airframe shape? Make a female mold? Usually you would just make a core, skin it, and bag it.