When water on land or in the ocean evaporates - turns from a liquid to water vapor - it rises. The water vapor cools and turns back into a liquid in the shape of tiny droplets. The result is clouds, unless it's on the ground - then we call it fog. When enough droplets get together they fall to the ground as rain or if it's very cold, they freeze and fall down as snow, sleet or hail.
Clouds play an important role in the energy balance of Earth. They cool the earth by reflecting sunlight back out to space. How else do you think astronauts see where they are going? More importantly, clouds replenish our water supply. It's a never-ending cycle but one that keeps the earth balanced.
You can tell a lot by looking at a cloud's shape, size and texture. Clouds are put into categories according to their shape, how high they are in the sky, their size, how fast and in what direction they are moving, etc. The three different types of clouds are high clouds (because they are high in the sky), medium clouds and low clouds (just over 10,000 feet high or 3 km.)
