General relativity is a theory that explains how gravity works. Imagine a stretched-out sheet where objects sit. When a heavy object is placed on the sheet, it creates a dip, causing smaller objects to roll toward it. This is similar to how planets move around the Sun. In reality, it's the mass of an object that curves spacetime, making objects move in certain ways. General relativity helps us understand how things move in the presence of gravity, like why Earth orbits the Sun or why light bends around massive objects like stars.