Explain in a simple way, how water erosion by groundwater can form a cave?

Groundwater can cause erosion through chemical weathering. First, water that sinks into the ground mixes with carbon dioxide to form carbonic acid, a weak acid. Carbonic acid can break down limestone. Some of the limestone changes chemically and is carried away in a solution of water. This gradually hollows out pockets in the rock. Over time, these pockets develop into large holes underground-caves or caverns.