What is a atom and what do atom do in the world

In all atoms, the number of protons and the number of electrons is always the same. The number of neutrons is very roughly the same as the number of protons, but sometimes it's rather more. The number of protons in an atom is called the atomic number and it tells you what type of atom you have.

Atoms make up everything in the known universe.

Explanation:

Atoms have different configurations, meaning that they have a different number of electrons surrounding the atom. There are actually two separate concentric rings around the atom, but that's not important to the answer. These separate atoms bind together to make molecules, which band together in different ways to form solids, liquids, gasses, and everything in between. In other words, we are all made up of around seven billion billion billion (7*10^27) atoms.