For general chemistry the primary focus is on Valence Bond Theory. This deals with
individual atoms and overlapping atomic orbitals. It also involves Lewis Structures and orbital
hybridization (hybrid orbitals).
Molecular Orbital Theory also involves the valence electrons but considers the entire molecule. In MO the electrons are delocalized and shared over the entire molecule. MO is better at explaining the energy of orbitals but not as good at explaining their shape.