What happens between Act 2, Scene 2 and Act 3, Scene 4 of "Macbeth"?I have been given a shortened text of Macbeth to write an essay about which...

There's a detailed summary at the link below, but here's the gist of each of the scenes you're missing:

Act 2, Scene 3: The Porter provides some light comic relief, and then morning comes and everyone discovers the body of Duncan. Macbeth reveals that he's killed both the porters at Duncan's door - whom Lady M was hoping to blame for the murder. Malcolm and Donalbain resort to escape, to England and Ireland respectively.

Act 2, Scene 4: A largely expositional scene that reveals that nature has gone haywire since the murder, and that Macbeth is to be crowned king at Scone. Macduff is going to Fife, and not going to the coronation.  Duncan's sons, Malcolm and Donalbain are suspected of the murder.

Act 3, Scene 1: Banquo suspects Macbeth of having done some "foul play" to get the throne. Banquo goes off riding, and Macbeth orders two murderers to kill Banquo and Fleance.

Act 3, Scene 2: Lady M asks about Macbeth's plan to kill Banquo. He doesn't tell her. Their relationship is starting to crack.

Act 3, Scene 3: A mysterious third murderer joins the original two. The three murderers kill Banquo in the dark, but Fleance (his son) escapes.