How do molecules move?
They move around in such a way that minimal energy is exerted.
Yes, just like us humans, molecules are "lazy"! They only move in such a way that they expend minimal energy. Why? The more unstable a molecule is, the more energetic it is. So high energy tends to mean unstable and thus unfavorable.
(However, high energy does not necessarily mean unstable)
They also vibrate in place.
Above absolute zero, their bonds always stretch in and out, and bend up and down (symmetric and asymmetric/antisymmetric stretches and bends).
OUT-OF-PLANE (OOP) BENDING