This video shows how to use a tire gauge. The first thing that you do is remove the valve cap off of the tire. Use the open end of the tire gauge. Put is onto the end of the valve. Don't use the other end of the gauge. The part of the gauge with the little round center piece in it is used to let air out of the tire. Once you have put the gauge on, push it firmly onto the valve. The air pressure in the tire will push the gauge measuring device out of the end of the tire gauge. You can look at that stick and read it to found out how much air is in the tire.