The three witches say foul is fair and fair is foul. lets fly away through the fog and filthy air. Macbeth is thane of cawdor because the previous thane has died. the witches call Macbeth "thane of glamis" and "thane of cawdor" and then " the future king"
Macbeth kills Duncan so he can be king and he can fulfill the prophecies that the witches told him but he doesn't think about putting the daggers back because he cannot bear to see what he has done.