The 1st apparition is a head wearing a helmet warning Macbeth that Macduff will return.
The 2nd apparition is a child covered in blood telling Macbeth that h ewill not be killed by anyone "of woman born".
The 3rd apparition is a child wearing a crown and holding a tree telling Macbeth that he's safe until the Great Brirnam wood moves to his castle.
The final apparition is a procession of eight kings with all resembling Banquo, foresahdowing that Banquo's prophecy of having descendants on the thrown is likely to come true.
After Macbeth meets with the witches the second time he becomes more paranoid and jumpy than before. He starts to get nervous that Banqou will search for revenge. However he also starts to doubt the truth of the witches prophecies because he doesn't understand how anyone could be born "for none of woman born" or how trees could attack him.