Here they are shown entering the Gate of Hell (to hear the inscription over the Gate click on the box on the listen box to the left). Once inside, they shall first pass through the region where the souls of the uncommitted (those who lived their lives without doing anything notably good or bad) reside. They shall then be ferried by Charon across the river Acheron into Hell proper. Virgil is the right-hand figure in blue, Dante the left-hand one in grey.
Notice how the greenery framing the outside of the gate contrasts with the bleak panorama of fire and ice inside. If you look carefully you can see tiny figures in torment on the hills. These successive hills represent the different circles of hell, where the souls of people guilty of different sins are punished in an appropriate manner. Those guilty of the sin of lust, for example, are buffeted about by the winds of passion and desire in the second circle.