If you're curious about the basics of grafting fruit trees, pick up the March/ April issue of Grit magazine, or take a look at the article on-line:
http://www.grit.com/Trees-and-Shrubs/Teach-Fruit-Trees-to-Multitask-with-Grafting.aspx
I interviewed a friend of my father's back in Ohio when we visited last July. Mr. Whitaker has well over one-hundred varieties on roughly 20 trees. He's been perfecting his hobby for decades, and is a walking encyclopedia. It was a treat to visit with him, and hear the different stories around the apple varieties.
I have a handful of scions cut from the apple trees in our yard. I'm going to give grafting a try again this year for practice, and hope to secure different apple types next season. Hopefully this spring the weather will cooperate a little better. Last year, the temperature dropped to a record breaking -8 three days after my grafting attempt. Not surprisingly, they didn't take.