what happens if we cover a burning candle with an inverted glass jar?why?

You have basically described the Bell-Jar experiment used to prove the existence of Oxygen being required for combustion and that it occupies approximately 20% by volume of the atmosphere at sea level.The water level rises because the Oxygen combines with the carbon to from CO2, and hence a partial vacuum is created inside the jar to the extent of the space occupied and the pressure exerted by the oxygen.

It stops burning because lack of  oxygen in jar ...............WITHOUT O2 FIRE DOSE  NOT EXISTS...............