The sun is at the center of the solar system. In fact solar means relating to the sun. All objects in our solar system orbit around the sun. They are held in by the sun's gravity. The sun is a star which means it makes its own energy. The sun is a ball of two gasses, hydrogen and helium. The sun is about a million times larger than Earth. The weight of the sun on its interior (inside) creates such a strong force that it combines or fuses atoms. During this process, energy in the form of radiation (heat and light) are given off. This process is called fusion. The sun's radiation (energy from heat and light) are what provides heat and light energy to the rest of the solar system. At 93 million miles from Earth, it takes about 8 minutes for sunlight to reach Earth while traveling at the speed of light (About 182,000 miles a second*).
Without this energy from the sun, life on Earth would not be possible. It gives us light, heat, and food. Our food comes from plants which have the ability to convert the sun's energy to sugars in a process called photosynthesis. All things must come to an end and in about 2 billion years from now, the sun is expected to die out (When the fusion stops). It will then expand to almost where Earth is today (And will be dark).
The speed of light is the fastest something can travel.