Gas is a state that substances can be in. Other states substances can be in are liquid and solid. The air around you is a mix of gases, and when you boil water the bubbles are the water itself turning from a liquid into a gas. Helium balloons are filled with another gas that most people are familiar with - helium is lighter than air so helium balloons rise up.
A gas can (also called a jerry can) is a container used to store and carry fuel like gasoline or diesel. It is usually made of plastic or metal and has a handle and a spout for pouring.
You might use a gas can to fill up a lawn mower or take extra fuel with you on a trip.
You gather things when you bring several of them to the same place. A gathering of friends is a group of friends getting together. The person in the picture has gathered a handful of berries.
