A planet is a large celestial body that moves around a sun. There are eight planets in our solar system. Our Earth is one of them. There are also stars outside our solar system that have planets. They are called exoplanets.
It is easier to remember the planets in our solar system with this sentence: "My father explains our night sky to me every Saturday." The first letters of the words are the same as those of the planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The order is from the sun.
A planet reflects the light of the Sun, so some planets can be seen from Earth in the night sky. An old German name is "Wandelstern" because planets "wander" a little further in the night sky each night in relation to other stars. Unlike stars like the Sun, planets do not shine by themselves.
The four planets closest to the Sun are Mercury, Venus, Earth and Mars. They are called rocky planets because they are made of solid material. Beyond Mars, even further from the Sun, the asteroid belt has been discovered. In this area there is no planet, but many smaller chunks of rock. These are the asteroids.
The four other planets in our solar system are outside the asteroid belt. They are called Jupiter, Saturn, Uranus and Neptune. These gas planets have a solid core, the rest consists of gases. Jupiter is by far the largest planet in the solar system. Smaller celestial bodies, the moons, orbit around many of the planets.