Our current understanding of the strong interaction of hadrons is that they are described by QCD, but we know very little about the physical states of the theory. Until we can predict the properties of the physical states of the theory and confirm these predictions by experiments, we can hardly claim to understand QCD, which has implications beyond hadron physics. Some essential properties of colour dynamics (QCD) and the salient features of quark model for hadrons are also described. The basic approach of quantum mechanics like general consequences of the Schrodinger equation, Virial and...