think of these numbers this way: your giving directions to get to the electrons. the "n" tells you what outer layer it is located. so for sodium we have 1, 2 or 3!!

so your "l" tells you the shape of the orbital that the electron is located. it starts with 0 and goes all the way to n-1. your S subshell is 0, your P subshell is 1, your D is 2 and so on. sodium can have 0 or 1 depending on which electron we are talking about.

so the "ml" is now the location of the electron in the subshell (the orbital). its from -l.....0....+l

S has l=0 and its ml=0

P has l=1 and ml= -1, 0, +1 (the three possible spots/orbitals for the electron to be located)

D has l=2 and ml= -2, -1, 0 +1, +2 (5 possible spots)

and so on

hope that helped