There are four main parts to the water cycle: evaporation, condensation, precipitation, and groundwater run-off.
Evaporation is the process by which a liquid changes into a gas. Evaporation requires energy. When energy is extracted from the atmosphere in order to evaporate water, the atmosphere cools. Evaporation is important because it’s how water vapor, which is necessary for clouds and precipitation, enters the atmosphere. (Another way that water vapor can enter the atmosphere is through transpiration. This is simply the evaporation of water through plant membranes.)
Condensation is the process by which a gas changes into a liquid. As water vapor rises in the atmosphere, it expands and cools. If it cools enough, it will condense into clouds, fog, dew, or frost. Condensation releases the energy that was used in evaporation, warming up the atmosphere again.
Clouds are made of millions of tiny water droplets that have condensed from water vapor. Inside the cloud, water droplets collide with each other, forming larger droplets. Eventually, the water droplets become large enough that they cannot stay suspended in the cloud. Then they fall as rain, also known as precipitation. If it is cold enough, the water droplets will form ice crystals. When the ice crystals collide, they form bigger ice crystals. Eventually these will fall as snow, also precipitation.
Precipitation falls to the surface, where it can return to the ocean or be absorbed into the ground. If the ground can’t absorb any more water, the precipitation runs off into a stream, where it eventually returns to the ocean.