How are evaporation and condensation related to saturated air above a flat water surface?

When u give energy to water in the form of Heat , all water molecules does not receive equal energy. Some water molecules have more energy than average energy of water molecules in a container , they will escape in to air in the form of Evaporation.

When u closed the container with a plate , the evaporated molecules condensed in to water droplets after hitting no of walls in container (no chance for escape) and enter in to container again.

After some time some molecules are evaporating and some molecules are condensing , at a certain stage no of molecules get evaporated becomes equal to no of molecules get condensing.

This is the point of Saturation. Air also takes some finite amount of humidity in to it , it depends on ambient air temperature.