Condensation is the process by which water vapor becomes liquid.It is the opposite of evaporation.
* Water vapor is the water in its gaseous state.
*Evaporation is the process by which water is converted from its liquid form to its vapor form.
A simple experiment to understand the concept of condensation.
1.Take a Thermos Flask(Vacuum Flask) and a Big Ladle.
2.Put the ladle in the cold water.
3.Then remove the lid of the vacuum flask.Fill the flask with hot water and place the ladle over the mouth of the flask.
4.Now you can note the water droplets falling off from the ladle.
5.Water droplets are formed when steam from the the vacuum flask touches the cold surface of the ladle.This is known as Condensation.
6.How rain is formed? When the accumulation of this droplets become plentiful,they fall as rain.
In Simple Words, Condensation occurs when warm air comes into contact with cold surface,which is at a lower temperature.
In other words,Condensation is the formation of liquid drops of water from water vapor. It is the process which creates clouds, and so is necessary for rain and snow formation as well.