Rain is the result of water droplets gathering together in clouds and gravity causing the water droplets to fall as rain. Warm air has more water droplets than cold air.
Rain is part of the water cycle. Air contains invisible moisture called water vapor. This is apparent on warm, humid days.when the air is thick with water vapor. Because warm air can hold more water vapor than cooler air, when the air becomes cooler, excess water vapor is condensed out as water in the form of water droplets. These water droplets are carried up into the clouds and as the clouds become heavy, rain may fall.
Water droplets inside clouds either grow on their own or join up with other droplets to become drops. Millions of drops form in clouds and the clouds can only hold so much water before they become too heavy to hold more. Both gravity and the weight of the water play a part in a rainstorm.
When rain begins to fall, not all of it makes it to the surface. Some of it is blown around and evaporates and some ends up back in the cloud. It will continue raining as long as water continues making the clouds heavy.