Why are clouds flying?
Clouds appear to fly or move across the sky because of the movement of air currents, particularly wind, in the atmosphere. Clouds form when moist, warm air rises and cools, causing water vapor to condense into tiny water droplets or ice crystals, which are the primary components of clouds. These water droplets or ice crystals group together and create visible clouds.

The movement of clouds is primarily driven by the wind. As air currents and wind blow at different altitudes in the atmosphere, they carry the clouds along with them, causing the clouds to move across the sky. The speed and direction of cloud movement depend on the strength and direction of the wind at the altitude where the clouds are located. Additionally, the movement of clouds may be influenced by local factors such as topography and temperature variations.

In summary, clouds appear to be flying because they are carried by the movement of air currents, especially wind, in the atmosphere.
That explains why they move/fly, but why don't they fall ? Aren't they subject to Earth attraction that should make them fall ?
Though clouds are heavy, they consist mostly of tiny water droplets and these droplets are hardly affected by air. Since clouds are so high, warm blankets of air below it rises, lifting the tiny water droplets in the sky. However, when it rains, the tiny water droplets merge and become heavier, being able to overcome the upward lifting force of the warm blankets of air and fall.