You're likely thinking of Kepler's First Law of Planetary Motion, not Johannes' First Law. Johannes Kepler was the astronomer who formulated these laws.

Kepler's First Law of Planetary Motion states:

* The orbit of every planet is an ellipse with the Sun at one of the two foci.

This means that the planets' orbits are not perfect circles, but rather slightly elongated ovals. The Sun is not at the exact center of the ellipse, but rather off-center at one of the focal points.