If you open up the Esc menu in wow and hit Key Bindings it will bring up a list of all of your keys and what they are bound to. I know that you can actually bind keys directly to a skill via a mod or what not but the easiest way would be to bind alt + x or whichever key you want to one of your action bar thingos. Say you wanted to use the very first slot on your bottom left actionbar you open up your spellbook and drag a spell onto it. Then open up key bindings (esc > key bindings) then find Bottom Left Action Bar 1 and hit the set key button. You then press alt + x or any combo you want and you are good to go. Hope that helps.