How Do Symmetry and Overlap Determine Molecular Orbital Interactions?

[Juche]

How do you determine the symmetry of the orbitals and whether they overlap in a molecular orbital diagram?

 

[chem_tr]

Well, s orbitals are spherical, so they can overlap with any orbital (s and p, and even d). p orbitals are not spherical, so they only overlap with same face-looking orbital; for example, two p orbitals, after losing one by overlapping with s orbital, have no common symmetry other than themselves; they overlap to give a pi bond.

I know this is hard to tell without a diagram, it tells better than me.