For example, the electrons in nitrogen start out in the 1s orbital then the 2s and then they occupy 2p. Aufbau's principle is the reason why the electrons must occupy the lowest energy level first.
Pauli Exclusion Principle- Atomic orbitals can have two electrons, and these two electrons must have a opposite spin.
An example of the Pauli Exclusion principle in nitrogen would be found in orbitals 1s and 2s. There are two electrons in each of these orbitals and one is moving clockwise while the other must be moving counter-clockwise because it would not be stable if bother were moving the same direction.
Hund's Rule- With orbitals of equal energy, one electron occupies each orbital until they all contain one electron.
For example, if you are doing the orbital diagram for nitrogen it would utilize Hund's rule because it does not completely fill the p-orbital.
