The Sun is the center of our Solar System. It is a yellow main-sequence star but very small for a star.
The sun is over 109x the size of the Earth, which equals a diameter of 1,392,784 km. It fuses Hydrogen into Helium for tons of energy. A single solar flare has enough energy to cause a major blackout. The Sun has >8 planets orbiting it. It is not a solid, liquid or gas, but a fourth state called plasma. It is essential to the survival of every living thing. So if the Sun suddenly disappears, plants will die, and sometime after then herbivores will die.
The Sun has several layers. The first, other than the core, is the radiation zone. Outside the radiation zone is the convection zone, where convection (rising and setting gases) occur. Then is the photosphere of the sun. The corona is hotter than the photosphere and is the Sun's outer atmosphere. The corona extends out to 3 times the Sun's diameter.
The hydrogen in the core would be exhausted (burned out) in 4 billion years. In 5 billion years, The Sun would grow in size and cool in temperature, becoming a red giant and swallowing Mercury, Venus, and probably the Earth in the process. In 10 billion years from now, the Sun's layers will become a planetary nebula (a cloud of gas) and the core will turn into a white dwarf.