In 2013, the BESIII collaboration in China and the Belle collaboration in Japan reported the observations of four-quark states. In this seminar, the constituent quark model and the diquark are introduced. Some structure and dynamics of the baryons, four-quark states and pentaquark states in terms of diquark are reviewed. The candidates of four-quark states and pentaquark states are given and some explanations in the normal quark model are given. In particular, the diquark cluster is examined in the strong decays of baryons with one heavy quark in the 3P0 model.