Tree staking kits are available at most nurseries and home improvement stores, and are beneficial for young trees. They provide support, protection from strong winds, and help the tree grow straight.
You can also make your own stake using untreated landscape lumber, a length of rope, and a piece of rubber hose or other bendable pipe material. Drive the lumber into the ground at an angle away from the tree in the direction you’d like to train it (if the tree lists south, for instance, place the stake north of the tree). Feed the rope through the hose; wrap the hose around the trunk just above the lowest, strongest branch; then secure the rope to the stake, tightening until the tree is straight. Do not tighten the rope too much; the tree should be able to move with the wind.
Title: Espalier: How to Train Fruit Trees
Author/Source: Gardens Illustrated
Description: Step-by-step instructions for training fruit trees into espaliers and other shapes. Includes pictures.
Title: How to Espalier Fruit Trees
Author/Source: Gardener Scott
Description: A 10-minute explanatory video discussing how to train and prune fruit trees into espaliers.