The Chorus is roughly like the peanut-gallery. In Antigone the Chorus is made up of a group of old Theban men. They're probably old men because most of the young ones have just died in battle. Also, they represent in some way the deeply embedded patriarchal (male-dominated) society that Antigone defies.
In Antigone the Chorus at times directly affects the action of the play. Though they at first seem to be totally on the side of their new king Creon, they begin to urge him to be more moderate. It's at their pleading that Creon decides not to sentence Ismene to death along with her sister. The old men of Thebes also practically insist that Creon take Teiresias's advice and free Antigone. Creon, of course, finally agrees to do this... but unfortunately it's far too late.
The main functions of the Chorus are to comment on the action of the play, give back story, and to connect the play to other myths. Sophocles also uses the Chorus to expound upon the play's central themes. In Antigone we get choral odes on everything from the triumph of man over nature, to the dangers of pride, to the hazards of love.
As in every ancient Greek tragedy, the first time we hear the Chorus is when they sing their parados or entry song. Parados looks a little bit like the modern word "parade," right? This is probably no accident. When the Chorus performed the parados they would "parade" in, singing and dancing with a bunch of fanfare. The actual word "parados" comes from the name of the corridor or archway through which the Chorus first entered.
In Antigone, Sophocles uses the parados to give back-story. The Chorus sings all about the terrible battle that has just been fought. We also get the sense that the people of Thebes are furious at Polyneices for betraying and attacking them. This helps to strengthen Creon's position about the traitor's burial.
Overall, the parados in Antigone is a joyful celebration of victory. This is, of course, super-ironic. The audience has just watched the prologue, in which Antigone declares her intentions to defy the state. Though Thebes has just defeated an external enemy, the new order represented by Creon will be challenged almost immediately by an enemy from within.
The next time we hear the Chorus is the First Ode. This little ditty just happens to be the most famous choral ode in all of Greek tragedy, and is popularly referred to as the "Ode to Man." In this celebrated ode the Chorus sings about all the wonderful accomplishments of man. The word "wonderful" in Greek is deinon. It can also describe something that is terrible. In a way, the word means both wonderful and terrible at the same time. But how could all of man's accomplishments be both of those things at once?
Let's take a look at the achievements that the Chorus lists. Humanity has: built ships to conquer the seas, crafted plows to tame the earth, bent animals to his will, raised houses to defeat the rain and the snow. Do you notice a common thread here? Nearly everything is about humanity asserting its will over nature. This echoes the basic conflict of the play.
Creon represents the state or man-made civilization. Antigone represents the primal will of the gods, a.k.a. nature. The storm outside of Thebes and the auguries of Teiresias hint that nature is offended by Creon's actions and stands on the side of Antigone. When all of Creon's family members kill themselves by the end of the play, it's as if nature itself is taking payment for his sacrilege. In a way, all of man's accomplishments could be seen as being just as terrible as they are wonderful. Each time we take a step forward, we separate ourselves father from the place that we began.
The Chorus ends the "Ode to Man" by praising the laws of the city. They disdain anybody who would want to bring anarchy back to Thebes:
Passing the wildest flight thought are the cunning and skill,
That guide man now to the light, but now to counsels of ill.
If he honors the laws of the land, and reveres the Gods of the State
Proudly his city shall stand; but a cityless outcast I rate
Whoso bold in his pride from the path of right doth depart;
Ne'er may I sit by his side, or share the thoughts of his heart. (368-375)
After the ode concludes, it takes Sophocles about two seconds to lather on the irony. Who should show up in chains just as soon as Chorus gets done talking junk about anarchists? Why it's Antigone—everyone's favorite protagonist and anarchist extraordinaire. When Antigone appears just as the "Ode to Man" concludes it's almost as if she's the god's answer to the great hubris (pride) shown in the Chorus's song.
Sophocles uses the second choral ode to relate the tragic history of Oedipus's family. This ode complements the scene before in which Ismene attempts to go to her death along with her sister Antigone. In the third choral ode the Chorus sings of the hazards of love. This is a comment on the previous scene where Haimon begs for the life of his beloved Antigone.
The fourth ode gives the audience some trivia about other mythic figures who've been entombed. The tone of the terrible tales in this ode seem to show that Chorus is beginning to really pity Antigone. By the end of the play the Chorus has totally changed their tune. These same old men who were previously celebrating man's mastery over nature are humbled in the face of the gods.
Like most all ancient Greek tragedians, Sophocles divides his choral odes into strophe and antistrophe. Both sections had the same number of lines and metrical pattern. In Greek, strophe means "turn," and antistrophe means "turn back." This makes sense when you consider the fact that, during the strophe choruses danced from right to left and during the antistrophe they did the opposite.
Sophocles may have split them into two groups, so that it was as if one part of the Chorus was conversing with the other. Maybe the dualities created by strophe and antistrophe represent the endless irresolvable debates for which Greek tragedy is famous?