How does molecular orbital theory explain CH4?
Methane doesn't illustrate the difference very well, but the difference is nicely illustrated with benzene. Valence bond theory would have the electrons in the "double bonds" isolated between atoms as so:



But the electrons in the "double bonds" are not isolated in three double bonds but distributed equally over all 6 carbon atoms. Valence bond theory tries to wiggle out of this dilemma by posing the Kekule resonance structure:



which still belies the situation. The double bonds don't "resonate." The extra 6 electrons are distributed in one aromatic molecular bond (with three degenerate orbitals) evenly over the 6 carbon atoms.