The witches are brewing a stew that is going to bring trouble to humanity. They use many exotic ingredients including snakes, salamanders, and owls.
Macbeth enters and asks the weird sisters what is going to happen to him next.
The witches show Macbeth apparitions that "guide" him. They are giving Macbeth a sense of security because they are telling him all these impossible things that won't ever happen. Therefore he will never be defeated.
Macbeth is very frusterated because he feels that he needs to kill Macduff to save himself from being caught. He also blames himself for being hesitant on doing it earlier.