The universe is commonly defined as the totality of everything that exists including all physical matter like the planets, stars, galaxies and the contents of intergalactic space and energy.
The study of universe is known as cosmology.
The universe comprises of billions of galaxies.Galaxy is giant assemblies of stars, planets, gases, and dust. These galaxies are made up of millions of stars held together by the force of gravity and these stars account for most of the masses of the galaxy. Andromeda is our nearest Galaxy.
Our own galaxy is called the Milky way (The Akash Ganga) and it contains about 300 billion stars and one of these is our sun. Planets and other objects go around the sun and make up the solar system with the sun at the centre.