Hello wendalore, imagine that you are climbing up via a slope and then by the steps. On the slope you can place your foot at any height. Hence all heights are possible. This is what we call continuous change. But as we climb up using steps, there are only certain heights at which we can place our foot. Hence the heights are only in discrete values. In between any two discrete values no other value is possible. In same way, energy emitted by a source is only in discrete quantities. So any amount is not possible. It will be an integral multiple of some fixed value. This fixed value for a monochromatic source (single frequency) will be hv, here h is Planck's constant and v is its frequency. So hv, 2hv,3hv 4hv and so n hv, where n is an integer are possible energy coming out of the source. But 1.2 hv is not possible. 1.5 hv is also not possible. This means the packet hv cannot be further split up. One more example for quantization is the charge of the proton or electron. The least value is found to be 1.6 * 10^-19 C. You cannot get 0.6*10^-19 C. or 0.8*10^-19C for any proton.
So Max Planck using this quantum idea he was able to solve the riddle behind the observed facts of black body radiation. Hence quantum mechanics. Only using quantum concept we can give proper explanation for photo electric effect and for Raman effect. Also Bohr applied the same quantum concept to find the radius of orbits in an atom and energy of the electron in orbits. As Albert Einstein stays as a revolutionary scientist by giving the theory of relativity so Max Planck another revolutionary scientist bringing out this quantum concept of energy. These two scientists are just like two eyes of the entire scientific realm.