What is the atomic number and what does the atomic number indicate?

The atomic number or proton number (symbol Z) of a chemical element is the number of protons found in the nucleus of an atom. It is identical to the charge number of the nucleus. The atomic number uniquely identifies a chemical element. In an uncharged atom, the atomic number is also equal to the number of electrons.

Atomic number is a number of element to show his situation in periodic table.

Atomic number indicate number of electrons

if you mean hydrogen and oxygen then water is the product