"Gas" can mean a few different things in American English:

1. Gasoline, which you put in your car to fuel it.
2. Gas, which is kind of like air. Air is a kind of gas. The Helium inside a balloon is another kind of gas. "Gas" contrasts with "liquid" and "solid".
3. Natural gas is a kind of gas (definition #2) that can be burned for heat or energy. This is what people sometimes use in their stoves.