Livre d'Or

To be completely honest, I could teach you this stuff, but your best bet will be to find your local SCA group. Ask around and find out who makes their own armor. Anyone who has made their own armor will know enough about leatherworking to teach you the stuff you need to know.

If you need help finding your local SCA group, let me know. I will certainly know how to track them down and may even have contacts there. :)