The  probability  of finding  out an electron at a point within an atom  is proportional  to the

Orbital wave function ψ is a mathematical function for an atomic orbital.

The square of the wave function, ψ² is called probability density and is always positive. Its value defines the probability of finding the electron around nucleus.

Principal quantum number defines the shell and majorly governs the energy and size of  the orbital. It is one of the solution obtained from ψ.