Bromination of benzene and other aromatic rings occurs via electrophilic aromatic substitution. The first step of the mechanism is the generation of the electrophilic bromine. This is accomplished by the reaction of Br2 with FeBr3 to form an FeBr4Br+ species that behaves as if it were an electrophilic Br+.
Draw curved arrows to show the movement of electrons in this step of the mechanism.