This is a large question for a limited format. I can give an overview of the first and last stages of Faustus's damnation. The first stage began when Faustus was "swoln with cunning, of a self-conceit" after having mastered all studies and sciences of his era. Undoubtedly, Faustus had a great and extraordinary mind used, again undoubtedly, for the wrong aims. Being "glutted now with learning's golden gifts," Faustus, based upon a real Doctor Johann Faust (1488), turned his considerable mental powers to magic, sorcery, "necromancy":
CHORUS: He surfeits [overindulges] upon cursed necromancy;
Nothing so sweet as magic is to him,
Which he prefers
Faustus's reason for this gorging on magic is that he desires things beyond the scope of humanity. He desires power over all things of earth;he desires deity (to be a god), which is ironic because (1) desiring to be like God is what caused Lucifer to be cast out of heaven to start with and (2) compared to the pantheon of gods, Faustus would be insignificant as a god. This was the beginning stage of his damnation.
FAUSTUS: All things that move between the quiet poles
Shall be at my command: ...
A sound magician is a mighty god:
Here, Faustus, tire thy brains to gain a deity.
The final stage of Faustus's damnation is a painful one. The Old Man comes to Faustus to try to lead him back to God through repentance. Faustus agrees with him and desires to seek repentance:
FAUSTUS: Accursed Faustus, where is mercy now?
I do repent; and yet I do despair:
Hell strives with grace for conquest in my breast:
What shall I do to shun the snares of death?
But--Mephistophilis appears, having heard the whole conversation, terrifies Faustus and threatens him grievous pain, thus Faustus recants his desire to be guided to repentance by the Old Man:
MEPHIST: Thou traitor, Faustus, I arrest thy soul
For disobedience to my sovereign lord:
Revolt, or I'll in piece-meal tear thy flesh.
FAUSTUS:Sweet Mephistophilis, entreat thy lord
To pardon my unjust presumption,
And with my blood again I will confirm
My former vow I made to Lucifer.
Thus begins the final stage of Faustus's damnation. He is later to confess to the Scholars what he has done and that he is in his last hour of life. They plead to pray with him yet, in concern for their safety, Faustus regretfully sends them away. Though Faustus sees sings outside in the sky that repentance might yet be his, he talks about it without knowing how to accept it. At the clock's stroke of midnight, the Devils come to remove Faustus to Hell. The Chorus concludes the tragic drama by warning to stay away from practicing magic, one of the "unlawful" things;
CHORUS: Cut is the branch that might have grown full straight,
Faustus is gone: regard his hellish fall,
Whose fiendful fortune may exhort the wise,
Only to wonder at unlawful things,
Whose deepness doth entice such forward wits ....