We propose and analyze a multifunctional THz graphene-based component with graphene elements placed on a dielectric substrate. The structure of the device consists of a disc shaped resonator coupled to three graphene waveguides that excite the dipole or quadrupole resonance of surface plasmon polaritons in the resonator. The graphene resonator can be magnetized by a DC magnetic field. This device fulfills filtering of the input signal and can be used as a power divider and also as a switch. The division mechanism of the T-junction can be provided by application of a DC magnetic field or by changing the Fermi energy of the graphene resonator via an electrostatic field. Some peculiarities of the two mechanisms are discussed. Numerical simulations show that for a central frequency of 7.12 THz, devices in the OFF state have the two output ports isolated from the input port at a central frequency of about 27 dB provided by the dipole mode resonance. In the ON state and the division regime, the transmission to the output ports is around -(4÷5)dB in the 3-dB bandwidth of about 12%.