Quantum numbers are used to describe each electron in an atom.  No two electrons in a given atom are allowed to be exactly the same, so each electron in an atom is fully described by four different quantum numbers.  They are the principal quantum number, the azimuthal quantum number, the magnetic quantum number, and the spin number.  As stated before, no two electrons within a given atom will have the same set of four quantum numbers.  The principle quantum number describes the energy level shell.  The azimuthal quantum number describes the subshell.  The magnetic quantum number describes the specific orbital, and the spin number describes the relative spin orientation of the electron.