Train trees when young, and prune when matured
While they are young, fruit trees need some initial training to establish a strong, well-balanced framework of branches that will be able to support future crops.
Once they mature, the trees benefit from yearly pruning during dormancy.
Regardless of the training method used, initial pruning is the same. If you've planted a 1-year-old unbranched tree (whip), you'll have to force it to develop branches at the desired level ― usually fairly close to the ground for easy picking. Heading back the trunk will stimulate lateral buds to grow into branches; cutting back to about 2 to 3 feet high is usually advised. The topmost shoot that develops will become the leader (the central, upward-growing stem).
If you're starting with a branched 2-year-old tree, it may already have a satisfactory leader and scaffold (primary) branches. These branches should be well spaced along the trunk and should radiate in different directions so they don't shade each other. If they're poorly placed, head back the tree as you would a whip and wait for new shoots to develop.