The thing about fairy tales is that there isn't an early, definitive, respected work which organizes the subject. For example, the Bible organizes Christian belief, but there is no Bible for fairy tales. Instead, there were a lot of loose, varying, short and not-very-interesting superstitions. Then literate authors came along, especially in the nineteenth century, and they took those ideas and produced fine tales from them.
1. Go to your public library, head for the encyclopedias and read the articles about fairy tales, myths & legends and magic.
2. Go to the shelves and start reading. 398, which is the number for folkore, is a good place to start. Other works will be in the fiction section under the author's name, which you will get in step one.
3. Don't overlook kids' books. They can contain fine writing and great concepts.
When I was a kid, my parents bought us the World Book Encyclopedia, which was accompanied by a set of books called The Junior Classics. The fairy tales in that set were wonderful! I was happy to learn that 30 years later my sister appropriated the Junior Classics on behalf of her daughter. Otherwise they would have gone to a thrift shop or worse.