The transfer of water between the atmosphere, the oceans, and the continents is known as the hydrologic cycle which involves water moving from the surface most importantly from the oceans to the atmosphere, over the land and everywhere in between. In phases of water, the earth is a sealed system, so water is not joined or withdrawn from the earth, it is simply transformed, transported, and even recycled.
Since the hydrologic cycle has no start or end, you can dive in at any step. A great place to start is in the oceans, where most water of the earth is stored.
