Resonances are commonly found in various quantum systems,independently of their building blocks and the kinematic regime of their appearance.Resonances are genuine intrinsic properties of quantum systems,associated with their natural frequencies,and describing preferential decays of unbound states.The effect of resonances and the non-resonant scattering states can be considered in the open quantum system extension of the nuclear interacting shell model.In these lectures,we will review the fascinating adventure of the last decade associated with the development and applications of the continuum shell model approach to bound and unbound nuclear states,nuclear decays,and reactions.