Maybe you're standing next to your friend and you hear him make a little farting noise. We're not talking about that kind of gas. Flatus is not funny. Not yet anyway. Gas is everywhere.
Gases are random groups of atoms.
There are solids where atoms and molecules are really compact. Liquids have them a little more spread out. One of the physical characteristics is that a gas can fill a container of any size or shape. Think about a balloon for a minute. No matter what shape you make the balloon, it will be completely filled with the gas.