Relative to electrons and electron states, what does the ml quantum number specify

Magnetic quantum number specify orientation of electrons in magnetic field and number of electron states (orbitals) in subshells..
Magnetic quantum number (ml) specifies the orientation in space of an orbital of a given energy and shape . Magnetic quantum number divides the subshell into individual orbitals which hold the electrons, there are 2l+1 orbitals in each subshell. For example, p orbitals (and their electrons) have three orientations in spase (px, py and pz).

They can measure  the amount of energy gained or lost