Question
when and how do you first prune a avocado tree ? my tree is only two ft tall all leaves, its my first tree, and do i have to have two trees for them to fruit. thanks, ken

Answer
Your tree is ready for it's first pruning.
Over-pruning (too much or too often) can stunt or stop leaf growth. Prune the first time to only shape the tree and thicken the branches. Cut just above the leaf node, (the area where the leaf is growing). The new growth will start there. After the first pruning, cut off only the very end leaf buds on the stem and, or branches. For tree limbs and main stem trunk, pruning promotes both fuller branches, and thicker, stronger leaves. Thin or spindly branches and stems make for a weak plant support foundation. Failure to prune often enough can create long winding weak branches and stems. Pruning allows the tree stem to thicken and grow more rigid.
Keep in mind this is a TREE. It will get to be 40 feet or more tall. No you don't need two trees to get fruit, but you will need to wait about five or more years for the tree to get mature enough to have fruit. If you live in a cold climate, you may not be able to plant this tree outside without it freezing in the winter. Most varieties will suffer damage if the temperature drops into the twenties.
This tree requires very bright light. The brightest you can provide. Put it outside in the sun, spring, summer, and fall, when danger of freezing is gone.  Give it as much light as you can inside in the winter.