What happens to air molecules when air gets warmer?

At increased temperatures, atoms and molecules exhibit more kinetic energy. This energy shows up as "vibration" in the atom or molecule. Those atoms and molecules also move around more in the "situation" they're in. As a liquid or gas, those particles that make it up will move around more within the volume of that liquid or gas. In a solid, the atoms or molecules will "buzz" increasingly as temperature goes up.