In the extract I'm going to analize, Satan is observing his new home trying to become aware of the new situation after his downfall and compares the new world to Paradise and feels lost because everything is different here: "the region, the soil, the clime"; there is only "a mournful gloom" all over the place, instead of the "celestial light" of the Paradise.
He is not glad at first to be there, but he soon rejects despair and accepts the new situation: ("Be it so", "Farewell happy fields where joy for ever dwells: hail horrors, hail infernal word”). Satan compares Heaven and Hell, appealing to sight, that also brings the cromatic contrast between these two opposite worlds: white for Heaven ("celestial light"), synonym of purity; black for Hell ("mournful gloom"), synonym of sin. So Satan can not believe his eyes, he is surprised to be sent by God to a desperate and dark land.
In the following lines Satan shows all his ambition, all his self-confidence and determination. He realizes that now he is the "new possessor" of a place far away from God's power and jurisdiction.
His ambition is to have a reign somewhere, no matter if that place is gloomy and horrible. He is great in the self-assurance of his strength: he has got "a mind not to be changed by place or time", a mind that "can make a Heaven of Hell, and a Hell of Heaven", so hell and heaven are only states of mind: Hell is in the mind because the mind can change the external world, and no viceversa.
Satan is the real hero of Paradise Lost, because embodies Milton’s Puritan ideals of independence and liberty since he is seen as a rebel fighting against the absolute power of a tyrannical God, just as Milton, defender of liberties, struggles his battle against a despotic king.
Even if Satan is the central figure in the passage, the presence of God is always felt. Satan never directly names him, but God is always in his thoughts. He feels to be equal to God in reason; he is inferior to him only in the power because God has got the strenght to be above angels, his "equals".