In Act III, Macbeth invites the members of his court to a banquet. As he enters, he sees the bloody ghost of Banquo seated at the table. He is shocked and terrorized by the sight. Knowing he himself had arranged for Banquo's murder, Macbeth attempts to shift guilt by asking which of the others had "done this," meaning which of them had killed Banquo. They, of course, are very confused because only Macbeth can see the ghost. Macbeth continues, this time speaking directly to Banquo's ghost:
Thou canst not say I did it. Never shake
Thy gory locks [bloody hair] at me.
It is clear to everyone present that Macbeth seems completely irrational. At this point, Ross tells the other guests to rise, noting that Macbeth is "not well." In other words, he tries to end the banquet and direct everyone to leave because Macbeth is acting so strangely.
Macbeth is sick (or not well) and lady macbeth is asking the guests to leave