Here it is how I studied them (looooooong time ago!!!)
Here we go:
1) The orbits and the energies of the electrons in an atom are quantized, that is only certain discrete orbits and energies are permitted. When an electron is in one of the quantized orbits, it does not emit any electromagnetic radiation; thus, the electro is said to be in a Stationary State. The electron can make a discontinuous transition, or Quantum Jump, from one stationary state to another. During this transition it does emit radiation;
2) The laws of classical mechanics apply to the orbital motion of the electrons in a stationary state, BUT these laws do not apply during the transition from one state to another;
3) When an electron makes a transition from one stationary state to another, the excess energy
4) The permitted orbits are characterized by quantized values of the Orbital Angular Momentum
Reference: H. C. Ohanian, Physics. Second Edition, W.W. Norton & Co., 1989, p. 1058.