In Act 3, what are the 4 most important events in this act of Macbeth?

Four most important events of act 3 are the
following:

1) Macbeth hosting his coronation
banquet;

2) Macbeth talking to two murderers and finalizing
the killing of Banquo and his son, Fleance;

3) The
murderers killing Banquo with Fleance escaping;

4) The
appearance and re-appearance of the ghost of Banquo at the
banquet.

The second part of your question sounds a bit
confusing to me. Still I am trying to make some comments on each of the four events
already mentioned:

1) Macbeth specially invites Banquo to
be present at the banquet as the chief guest and the latter promises that he would not
fail. Macbeth then speaks his mind in a soliloquy that reveals as to why he wants to get
rid of Banquo. The banquet later exposes Macbeth's villainy in the assembly of all
Scottish nobles.

2) As we see how Macbeth finds out two men
to antagonize them against Banquo, we understand that Macbeth can now work out his evil
designs by himself and in a very cleverly manipulating
manner.

3) As the rain of blows on Banquo's head dispatch
him to death, we see how Macbeth enhances his own doom. Banquo shall have to keep his
promise of attending the banquet in the form of a ghost born of Macbeth's own
terror-stricken mind, since Fleance has escaped.

4)
Banquo's ghost appears and disappears twice in the banquet scene. Dead Banquo thus
proves to be more potent a threat to Macbeth than the living Banquo. The ghost forces
Macbeth to betray his crime and prepares his way to doom as Macbeth resolves to meet the
witches to know 'by the worst means, the worst'.

Hope you
will find all this reasonably helpful.