The sun is a star. It is in the middle of our solar system. Our Earth is one of the eight planets that orbit the Sun. The sun is 150 million kilometres away from the earth. Even light needs about 8 minutes to get there.
Compared to the sun, all the planets are tiny. If you take all the material in the whole solar system together, almost all of it is the sun. The Earth, with its size, would fit inside the Sun far more than a million times. This makes the Sun similar in size to many other stars.
The sun consists almost entirely of gases. It is hotter than you can possibly imagine. If a satellite gets even a little too close to the sun, it burns up. Because of this heat, the sun emits light and heat like other stars. Some of it reaches the Earth. Thanks to the sun, it is bright on Earth during the day. Our moon and also the planets shine because they are illuminated by the sun. Sometimes the moon is exactly between the earth and the sun, so that it covers the sun: this results in a solar eclipse.
But the sun also emits many rays that would kill all life on earth if they were not stopped. But the Earth's magnetic field protects us from this dangerous radiation.