Explain Kepler's first law (Law of Orbits) for planetary motion.

(N/A) Law of Orbits:
All planets move in elliptical orbits with the Sun situated at one of the foci of the ellipse.
An ellipse is traced out by a planet around the Sun. The closest point is $P$ and the farthest point is $A$. $P$ is called the perihelion and $A$ is called the aphelion. The semi-major axis is half the distance $AP$ (denoted as $a$).
This law was a deviation from the Copernican model,which allowed only circular orbits. (The ellipse,of which the circle is a special case,is a closed curve).