Grafting, also known as "top working," is simple-but-essential technique that enables you to change the variety of fruit a tree bears. In this tutorial, Stephen Hayes of Fruitwise Apples Heritage demonstrates the rind grafting technique, a useful method for grafting over a sound-but-unwanted apple or pear tree.
With all kinds of grafting, the principles are the same. Cut the scion wood in late winter, store somewhere cool and not-too-dry (a polyethylene bag in the fridge is ideal) then carry out grafting operation in early spring when the new leaves are beginning to come out. Cambium to cambium contact is key.
Before attempting any sort of grafting, practice the technique with a small very sharp knife on waste wood until you become reasonably good at shaping the pieces to fit together well. Good timing, clean cuts that fit, cleanliness, and correct wound sealing are key to successfully grafting a fruit tree.