Most of the items here are made with veggie tan leather of various thickness.
There are many websites that will give you some good info like :http://kingsmerecrafts.com/ but this site will be a great resource.
As a beginner, I would suggest getting some of the ebooks that Tandy sells on their digital library: http://www.leathercraftlibrary.com/c-79-ebooks.aspx .
A few to think about:
ABC's of leatherworking, the art of making cases 1,2,3 or encyclopedia of saddle making. These are very foundational books that will get you up to speed pretty quick.