Clouds are just lots of drops of water all stuck together. When clouds get so full of water droplets that they can't hold any more, the water falls back to the ground as rain! Sometimes the water droplets freeze and fall to the ground as snow, sleet, or hail. Water or ice that comes from clouds is called precipitation.
Precipitation forms in the clouds when water vapor condenses into bigger and bigger droplets of water. When the drops are heavy enough, they fall to the Earth. If a cloud is colder, like it would be at higher altitudes, the water droplets may freeze to form ice