Precipitation is an integral part of the natural water cycle.
The air is full of water, even if you can't see it. Higher in the sky where it is colder than at the land surface, invisible water vapor condenses into tiny liquid water droplets—clouds. When the cloud droplets combine to form heavier cloud drops which can no longer "float" in the surrounding air, it can start to rain, snow, and hail....all forms of precipitation.
The amount of precipitation that falls is different all around the world. In deserts, such as in Chile, it may only rain one inch per year, while on some mountains in Hawaii and in India, it can rain more than 600 inches per year. That is almost 2 inches every day!
Some locations get rain all year long, and many other places have rainy and dry seasons, and only get significant rainfall during certain months of the year. Some places, such as Antarctica, really don't get rain, but they sure get a lot of snow, which accumulates as icefields and glaciers.
Precipitation is the "exit ramp" back to earth from the superhighway in the atmosphere that is moving water vapor and clouds all around the globe.