Why doesn't the flame just continue to burn underneath the bell, no matter how flat you crush it? The answer is air.
Fire is a chemical reaction between oxygen molecules and some kind of fuel. This reaction releases the heat and light that we call fire.
You held a burning stick up to a non-burning stick. Why do you now have two burning sticks? The answer is in the nature of fire.
Want to try an experiment involving water, fire, and a balloon? Learn about "The Fireproof Balloon" on this Moment of Science.
You can think of a flame as being like a kind of tent. Heat melts the candle’s waxy fuel, and turns it into a gas. This fuel gas floats away from the wick to fill the inside of the flame’s tent.