Most of the time, air has some water vapor in it. (Water vapor is the gas form of water: the water molecules are far apart. It’s also invisible. Steam is water droplets too.)
The amount of water that a given ‘parcel’ contains depends on its temperature. Clouds form when the water vapor is too much and the air cannot carry it anymore. A major way is when moist air rises it cools off. Cooler air can’t carry as much water. That water has to go somewhere, so it condenses. One way to reverse it is heating that. That’s how sun “burns off” fog. So the cloud water is still there, it’s just in the form of invisible water vapor.
https://climatekids.nasa.gov/cloud-formation/
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