Question

about formation of clouds

Answer 1

Clouds are formed when air containing water vapor is cooled below a critical temperature called the dew point and the resulting moisture condenses into droplets on microscopic dust particles (condensation nuclei) in the atmosphere.

Answer 2

Dear Vignesh, if you understand terms like dew point etc. you can follow Aparna74004's answer but if you are in a junior class, this might be helpful.
Clouds are formed when water vapour from seas, rivers, lakes and other water bodies condenses to form tiny water droplets at a low temperature high up in the atmosphere.These tiny droplets then come together to form clouds. Hope this was helpful