Skyrim staff

how do you recharge staffs in skyrim when you use them. all my staffs say they are out of energy. i know you have to buy gems to recharge them but how do you do it.
Answer #1
Use a soul gem.
Find the staff in the inventory and press T to charge it.
Answer #2
With a soul gem in your inventory (of the right size), cast soul trap on the target and kill it, this should charge the soul gem, which you then should select from your inventory to recharge your chosen weapon.