There are two sections in the vocal cords: Primo passagio (which is the transition between speaking voice and raising one’s voice) and the Secondo Passagio (which is the transition point between chest and head voice). The latter is usually at middle C for baritones. Here the voices overlap when singing. So you practice chest and head voice separately and then the smooth transition, so you sing mixed voice or bridged voice.
(Tenors also have this, but the transition point is usually at the F.)
Have fun practicing!