Gotta rush, but basically matter = energy. All matter has a wave and particle duality. Electrons in orbit around an atom exhibit both wave and particle characteristics. Quantum mechanics refers to the 'quanta' (discrete numeric multiples of a constant, such as 1h, 2h, 3h etc) of energy states of a wave/particle such as an electron. It descibes (for example) how electrons can only exist in discrete quantum states when bound to an atom. This reflects the wave-like nature of the electron rather than the particle nature, because it seems more like a standing wave wrapped around the atom than a single particle orbiting the atom. Only relevant at atomic and sub-atomic scales though, not in the day to day world that we all experience.
