What is the Sun?

The sun is one of the billions of stars that permeate the Milky Way Galaxy that was formed about 4.6 billion years ago. It is a giant ball of burning hydrogen and helium gases which account for 70% and 28% of its mass respectively. The remaining 2% is made of iron, oxygen, nitrogen, silicon, magnesium, carbon, and neon.
With a diameter of 1.39 million kilometers, the sun is the largest and heaviest object in the solar system - it is located at the center and accounts for 99.8% of its mass. This translates to a strong gravitational pull that keeps the planets in the solar system revolving around it. It is, however, important to note that the sun is very small compared to other stars in the Milky Way Galaxy.
The sun's surface has a temperature of about 5500 degrees Celsius while the core stands at 15 million degrees. These high temperatures make the sun particularly important to planet earth as it acts as the source of energy needed to sustain life. Scientists believe that the sun has enough nuclear fuel to continue powering it for the next 5 billion years before it starts growing bigger.

To understand the sun, let's imagine a big ball of hydrogen sitting in space. Now, it's all gravitationally attractive, so therefore it falls towards the center of the ball. This means that pressure begins to build up as more hydrogen is crammed into the central area, however it keeps getting compressed more and more because there's lots of force inwards from the gravity of the outer layers.
Eventually, the pressure gets so large that nuclear fusion is an energetically favorable process. To simplify, it just means that fusion will happen only when the pressure is very high. As soon as the pressure reaches this level, it begins. This nuclear fusion pushes everything outwards because the immense energy released gives the particles nearby lots of energy. This heat also propagates outwards, helping to heat all the rest of the gas, though some of it is already pretty hot from pressure alone.
The sun is a big ball of hydrogen with two main forces: gravity crushing the center and pulling the outside in and pressure from nuclear energy pushing outwards. These forces end up being balanced, and you have a stable star. The gas is very very hot from all the energy, but nuclear fusion only occurs in the middle bit. Even when the star is old and dying, nuclear fusion only occurs somewhat near the center, and the outer layers will never fuse.

The Sun is the medium-sized star located at the center of our solar system, around which the planets in our solar system, including Earth, revolve. The Sun is comprised of immensely hot gases, mostly hydrogen (approximately 70%) and helium (approximately 28%). The Sun provides warmth and energy to every planet in our solar system, with the heat from the Sun traveling even beyond the reaches of Pluto.
Life on Earth, through different means, harnesses the power of the Sun for energy. The energy of the Sun is produced through nuclear fusion. Plants use the power of the Sun through photosynthesis. Humans can harness the power of the Sun through the use of solar panels. This energy source is far more ecologically friendly than coal-based power sources. Without the energy and heat provided from the Sun, life on our planet could not exist.