1. lay the arm guard aginst your arm
2. reach through the top strap
3. Grab bottom strap and pull through top strap and hook to top button
4. Grab top strap and rap around and hook to bottom button.
You might do a little change and get some elastic, brade it and stick it through the holes and tie it off. Here is a couple of pics of what the elastic looks like installed. Leave some extra on one end so you can adjust for wearing bulky gear during winter.
If you are asking where you wear it here is a pic