Macbeth appears on stage and compares himself to a bear in a bear-baiting contest (i.e. he's in a serious jam).
History Snack: Bear-baiting is a blood sport that involves chaining a bear to a stake and setting a pack of dogs on it.
Elizabethans thought this was good clean family fun. Bear-baiting arenas were located in the same neighborhoods as the theaters, just in case anyone wanted to take in a play and then top off their day of fun with a little animal cruelty.
Young Siward enters and...quickly dies. Macbeth talks some evil smack over the dead body, to the effect of "your swords and weapons can't touch me because you're of woman born."
Macduff runs on stage looking for Macbeth and screams for the evil tyrant Macbeth to come out and show his ugly face.
Macduff is hot to kill Macbeth with his own sword because he'll likely be haunted by the ghosts of his wife and kids if he doesn't.
He begs "fortune" to let him find Macbeth so he can stab him in the guts.
Siward and Malcolm note that Macbeth's castle has basically been surrendered without a fight. They're winning battles with little effort, mainly because the people they're fighting aren't really trying. Even Macbeth's soldiers hate him. So. Many. Enemies.