Relativistic jet phenomena are most often observed in the vicinity of black holes, where the surrounding plasma accretion plays an important role in the formation of these jets. The presence of a magnetic field is crucial since it has a significant effect on the accretive behaviour of a plasma. Primarily, the magnetic field links the central source with the ambient plasma and can be considered as a set of wires which can transport energy toward the black hole and away by means of MHD waves. Moreover, the magnetic field is able to collimate the plasma flow, which gives rise to a relativistic jet formation. To investigate the behaviour of a magnetized plasma accretion around a spinning black hole we use a string approach, which allows to depict the magnetized plasma as a set of magnetic flux tubes/string. It turned out that the interaction of the magnetic flux tube with the spinning black hole leads to an energy extraction process, which is attended by a relativistic jet creation. The influence of the reconnection process on the jet evolution leads to the formation of plasmoids, which move outward from the central source and remove energy and angular momentum. This process can be repeated over and over and finally the jet structure is composed of a chain of plasmoids which propagate along the spin hole axis.