Refer to figure.
Rising air is the primary driver of cloud formation. As air is forced upward, it expands and cools adiabatically. If it rises sufficiently, it will reach its dew point, leading to condensation and cloud formation.

Humidity refers to the amount of water vapor present in the air. At any given temperature and pressure, the air has a maximum capacity for holding water vapor. Warm air can retain significantly more moisture than cold air. As the air temperature decreases, relative humidity increases, and vice versa. When warm, moist air cools, it eventually reaches a point where it can no longer hold all its water vapor—this is called the dew point. If cooling continues beyond this point, excess moisture condenses into liquid form, leading to the formation of dew, fog, or clouds.

In this scenario, relative humidity is already at or near 100% when condensation occurs, since the cloud has already formed. As the cloud rises, it cools due to adiabatic expansion, causing additional water vapor to condense into tiny droplets. This increases the concentration of water droplets within the cloud, contributing to further cloud development and potentially leading to precipitation if the process continues.