How does water erosion change earths surface?

In short: in many ways:

• Rivers carve the landscape by forming channels for themselves.
• Rainfall causes the dissolution of limestone and some mineral cements. In caves these sediments are deposited as stalactites and stalagmites.
• Frozen water (ice) carves the landscape as a glacier, forming distinct U-shaped valleys.
• Sea/ocean tides and waves cause coastal erosion

Water also causes weathering in various forms. All these factors cause major changes in the surface of the earth.