How do two or four ligands arange themselves around a central metal molecule?

Alright, a brief chemistry question here about how the MO theory predicts a ligand arrangement. All of the ligand-metal arrangements that I have dealt with so far are just six ligands around a central metal atom, but our book glances over two ligand linear and four ligand square planar/tetrahedral arrangements. The six ligands make sense because you get one s, three p, two bonding d orbitals, and three d non-bonding orbitals and it all works out with the number of electrons you have compared to the number of orbitals, but when I try to go back and redo the same thing for two and four, it doesn;t work out.

Could someone just explain what two or four ligand MO models look like, or point me to a resource with them?

Gracias
Threemae