The earth's surface is constantly changing. Mountains of rock are worn away by wind, water, ice, and even living things. As large rocks are broken into smaller rocks they are carried to new places by wind and rain. When rock fragments settle in a new location over time they are compacted into new rock formations called sedimentary rock.
Weathering is the name for the natural forces of earth that slowly wear away at rock formations. With enough time, rock can be carved by rivers and streams.
Erosion is the process of weathered materials being carried to a new location by natural forces like wind and water.
The Grand Canyon was formed by the Colorado River over the course of hundreds of millions of years.