There are three types of forms called liquids, gases, and solids. Simply put, they are "ordinary water," "water vapor," and "ice.
There is an order in which these forms change. In order for water vapor to become ice, it must first become water and then ice. Conversely, in order for ice to turn into water vapor, it must first turn into water and then into water vapor.
However, when the temperature of water vapor in the air suddenly drops below 0°C, it does not become water but ice. This is how servant is formed.
Thus, water vapor hidden in the air is suddenly cooled and suddenly becomes ice, which sticks to the ground and leaves.