I am growing an Avocado tree. I was told that the tree needs to be cut back. However, I am afraid of damaging it. My question is whether cutting back is recommended and how do I do this without damaging the tree
Avocados don't take the same pruning approach that you would with other trees. From a University of Florida Extension publication (PDF Link):
Most avocados don't need a lot of pruning. However, pruning avocado trees can be beneficial in some cases. Pruning these trees is different than pruning other trees, so there are a few things you should know beforehand. In general, avocado trees require an abundance of healthy foliage to assure high yields. In most cases such abundance is best achieved by pruning only when absolutely necessary.
Since avocado trees grow irregularly and different varieties have different growth habits, pruning methods will vary. Trees which tend to develop spreading canopies do best with a minimum of pruning. Tall, upright varieties, which become veritable "beanpoles" producing fruit high above the ground, can benefit from judicious training (heading cuts), especially during the first years of the tree's life. To prevent the upward growth of the main leader, the terminal buds should be removed. This stimulates the growth of lateral branches forcing the tree to spread out and become more compact.
Danger of breakage from wind is reduced and the fruit will be borne on limbs closer to the ground where it can be picked more easily. Excessive pruning of young trees will slow their growth since food producing foliage (food is manufactures in the leaves) necessary to the tree is removed. The yield of bearing avocado trees is in direct proportion to the amount of healthy wood and foliage on the tree. Heavy pruning does not increase fruit production but reduces it by stimulating new vegetative growth at the expense of fruit production.
As with any tree, if you do any pruning, be sure to follow proper pruning techniques, and understand how the tree will respond to each cut.