Answer:
Rivers start as a small body of water. As it is fed by rain, melting snow and ice, it grows larger and becomes a gully. If the right conditions are met and the gully is fed by more water, it becomes a large body of water - a river.
Step-by-step explanation:
Rivers usually start as a small body of water, known as a stream, that runs and flows down a mountain or a hill. If the right and optimal conditions are met, rains starts falling and feeds different streams that eventually meet and form an individual and larger body of water known as a large channel or gully.
This body of water grows larger as it continues to be fed by rainwater and snow melting (depending on the location) and becomes a river. Once multiple rivers are formed, they empty out into the ocean.