I'm glad you've asked about the hydrologic cycle because it is very important for climate, landscapes, transport of materials, and life. The hydrologic cycle is an idea that has been around for a long time and I'm not sure who actually thought of it. It was designed to describe the way that water moves from the oceans to the atmosphere to the land surface (or groundwater), and back to the oceans again.

Scientists observed that water evaporates from places like oceans and lakes and that it falls as rain and runs over the surface as rivers or under ground as groundwater. The hydrologic cycle was designed to explain how evaporation and precipitation and the water in streams, lakes, groundwater, and the oceans are all connected in a continuous cycle. Perhaps you could draw a picture of the major locations of water (oceans, atmosphere, surface water like lakes and river, and groundwater)and then draw connections between these locations to show the processes that move water from one of these locations to another (evaporation, atmospheric transport, precipitation, surface flow, and ground waterflow).

If plants draw water up from the ground and transpire (like breathing it out) it into the atmosphere, where would they fit in the hydrologic cycle? I also encourage you to look on the internet for the key terms Hydrologic Cycle. There are a lot of good websites with pictures and descriptions of how water moves between the surface, the oceans, and the atmosphere.