There is considerable variety in how quills are applied to leather, how edges are made, etc. The techniques varied somewhat with the tribe doing the work, both in terms of patterns used and how the quilling was done. William Orchard's book,Technique of Porcupine-Quill Decoration Among the North American Indians, will give you a good idea of how to go about it or you could take a class at Conner Prairie.
You can get a used copy of the book for about $8 including shipping on line through abebooks or other sellers. It's well worth having if you have any serious interest in this.
Tom