We all know that the sun is the center of our solar system, but in the Middle Ages, people believed that the earth was the center.
Models are a way to help us explain patterns that we see. When early astronomers looked into the night sky, they saw stars and even planets that looked as if they were revolving around the earth. The model that states that the earth is the center of the universe is called the geocentric model.
Later, astronomers found out that the earth is not the center of the universe, so they gave that ostentatious title to the sun, but they were also mistaken; it was the center of the solar system.
Even though the sun is the center of the solar system, it appears that it revolves around the earth, this is because of apparent motion.
Another example of apparent motion is when you are in a car, and it seems as if the countryside is passing you quickly, when in fact you are passing it.
Our solar system is just one of many of the solar systems forming the Milky Way. The Milky Way alongside other galaxies form galaxy groups. The reason they are attracted to each other is the same reason why we are pulled to the ground or why the earth is revolving around the sun; gravity.