Kepler’s three laws describe how orbital bodies move. The law of ellipses, his first law, states that planets move in elliptical orbits around the sun with the centre of the sun being the focal point. Kepler’s second law is known as the law of equal areas, it states that a planet traces equal areas in equal time periods.
Kepler’s third law, the law of harmonies, is more complicated. It states that a planet’s orbital period (the time in earth years that it takes a planet to make a complete revolution around the sun) is proportional to the size, specifically the semi-major axis, of its orbit.