The sun is at the center of the solar system, and gives us light and heat. The sun is a huge sphere of hot gas, which burns hydrogen and turns it to helium. When the sun does not have any hydrogen left to burn, it will start burn helium, but this wont happen until 4.5 million years later.
The constituents of the sun can be considered as the following: Hydrogen (92.1 %), Helium (7.8 %), Oxygen(0.061 %), Carbon (0.030 %), Nitrogen (0.0084 %), Neon (0.0076 %), Iron (0.0037 %) and other elements.