Using Crystal Field Theory explain how d orbital splitting arises in an octahedral field.

I am unsure of how to answer this question. Are they looking for an answer that states it's the orientation of the orbitals and that the orbitals are filled in a certain way depending on the complex? Thank you for your help in advance.

I have already answer this question before to some one else. So, here is what said...
In absence of any ligands, the 5 d-orbitals are all degenerate and lie at the same energy level.
For an octahedral field, 6 ligands at the 6 vertices of a regular octahedron will surround the central metal ion. The dz2 and d(x2 - y2) orbitals lie along the three principle perpendicular axis, while the three dxy,dxz, dyz orbitals lie in the plane between the three major axis.
As the 6 ligands approach the central metal ions, the ligands will interact with the central metal ions d-orbitals raising the energies of the dz2 and d(x2 - y2), and lowering the energies of the dxy, dxz, and dyz. Thus, the 5 d orbitals are split into two groups, one containing (dxy, dxz, dyz) and other containing dz2, d(x3 - y2).