Answer:
First understand how clouds form.
When moist air at 100% humidity cools the air can't hold the moisture and the water condenses into colloidal droplets which can stay airborne (bigger drops fall as rain). The mass of colloidal water droplets are clouds.
Dispersing clouds run this process in reverse.
As the air gets warmer from sunshine or from coming closer to the ground (as an air mass comes down, its pressure goes up and, by the gas laws, its temperature goes up as well) the warmer air can hold more moisture and the water in the cloud droplets vaporizes back into invisible vapour.