A hoop gun is a tool that helps people spray paint onto walls or other surfaces. It's called a hoop gun because it has a circular shape that you hold onto like a hula hoop.
When you want to use a hoop gun, you first put some paint into it. Then, you turn on the air compressor. This is like blowing air into a balloon - it helps push the paint out of the hoop gun and onto the wall.
When you start spraying the paint, you move the hoop gun back and forth. This helps spread the paint out evenly. You have to be careful not to spray too much paint in one spot or it might drip down the wall.
Overall, the hoop gun helps people paint things faster and more evenly than they could with a regular paintbrush. It's a useful tool to have if you need to paint a lot of walls or large surfaces!