Armando -- i really just learned how to do this by doing. i started by just going to walmart and buying the fiberglass kit they make. maybe few other folks can recommend a book. I imagine there are several out there.
I have purchased fiberglass products from these guys --
http://www.uscomposites.com/
the masking tape/cardboard method is just one i made up.
the green filler material is "Duraglass". Kind of a pain to sand, but good stuff. a few of the "pro's" here have recommended it.