Please make sure that the water line that runs to the faucet into the garage and the water line that runs to the faucet at the back of the house is turned off from inside the house. This is critical in the event of the outside pipe or outside faucet freezing.
The normal procedure for winterizing outdoor faucets is to close the valve on the inside of the house which is usually located a couple of feet from the wall where the water line runs outside to the faucet. Once this inside valve is closed, the faucet outside should be opened fully so any water remaining inside the pipe will drain to the outside. You can leave this faucet open all winter if you wish.
There is usually a small drain plug that is located on the side of the inside valve that leads to the outside faucet. This drain plug should be unscrewed and this will allow any trapped water to drain out. Make sure you have a bucket handy to catch the water that drains out. This picture below shows the inside valve with the drain plug.
If you have any questions, please let me know.