Clouds are formed by the tiny water droplets and ice particles that are so small and weightless which makes them to stay up in the air. The two main process that includes in the formation of clouds are, 

1. Evaporation and

    2. Condensation

The water or ice crystals travel into the sky through air in the form of liquid gas from the sources of water like ocean, river and lake etc, by the process called evaporation. When air rises in the atmosphere, under the low pressure it gets cold and cannot hold water vapour. These water vapour then becomes ice crystals and hence cloud is formed. 

 When water vapour has a particle to condense on,  it is easier for it to condense into water droplets. The particles such as dust and pollen which are called as codensation nuclei helps in the formation of cloud when enough water droplets condenses on the condensation nuclei. 

Types Of Clouds:

Coming to the types of clouds, the different types of clouds are divided into groups based on their height, appearance and characteristics. Clouds are formed on the basis of temperature and pressure. It's temperature and pressure decreases as the clouds rises, causing water vapour to condense. The air gets lighter and less dense when it is heated. As the air gets warm and rises, the form of cloud emerges above the mountains. The clouds are formed when the air is driven upwards at low pressure. 

There are 10 major types of clouds, namely 

1. Stratus
2. Cirrus
3. Cumulus
4. Altocumulus
5. Cirrocumulus
6. Cirrostratus
7. Altostratus
8. Nimbostratus
9. Cumulonimbus
10. Stratocumulus

Among these types, the most commonly seen clouds are stratus, Cumulus, Cirrus and Nimbus.

Stratus is a low level cloud which is just 6500 feet above. This cloud appears to be thin and looks like a white sheet covering the sky. Since it is thin, it produces snow. In mountains or hills these clouds appears as fog.

Cumulus is also a low level cloud is fluffy and looks like a white cotton forming different shapes. This cloud looks beautiful and is fun to watch. 

Cirrus is the high level cloud which appears above 16,500 - 45,000 feet. These clouds look feathery and are made of ice crystals.

Nimbus is a type of cloud which produces precipitation. The precipitation reaches the ground in the form of rain. These appears to be black (dark) and can be seen before it starts raining.