This concept delves into quantum particle transport at the nanoscale, with a particular focus on how electrons move through molecular circuits. The thriving field of single molecular electronics benefits from the unique electrical and other properties of nanostructures. It concentrates on single molecular junctions that serve as bridges between electrodes. In this context, the electronic correlation-induced many-body effect gives rise to resonant states. These states, along with conductance, depend on electron spin. Thus, the field acts as a bridge between quantum and macroscopic worlds, unveiling unique behaviors of electrons. Additionally, external factors, such as magnetic fields and voltages, offer means to control the electron correlation in these junctions.