What does Antigone wish to do with the help of her sister? Why does she wish to do this?

Antigone wishes to bury her brother, Polyneices, who has been killed in a battle with her other brother, Eteocles, and she wants her sister Ismene to help her. The problem is that Polyneices committed treason by attacking his home city of Thebes, and so the king of Thebes (who happens to be their Uncle Creon) has proclaimed that Polyneices cannot be buried, and anyone who is caught trying to bury him will be sentenced to...

Antigone wishes to bury her brother, Polyneices, who has been killed in a battle with her other brother, Eteocles, and she wants her sister Ismene to help her. The problem is that Polyneices committed treason by attacking his home city of Thebes, and so the king of Thebes (who happens to be their Uncle Creon) has proclaimed that Polyneices cannot be buried, and anyone who is caught trying to bury him will be sentenced to death.

So why on earth would Antigone want to bury Polyneices, at the risk of death? There are three main reasons:

1. Basic human dignity, under the premise that all people deserve to be buried after death regardless of their crimes. 

2. The gods demand their dead. Antigone tells us that the gods of Hades have something akin to a legal right to the souls of the dead, and leaving Polyneices unburied would cause his soul to be displaced and wander like a ghost rather than going to the underworld where it belongs.

3. Point 2 above leads to the effectual curse upon Polyneices' soul, which Antigone implies would become a family curse if she was capable of burying Polyneices but chose not to. She would be blamed for his wandering soul and the anger of the gods of Hades.

Even though it might seem prudent not to risk her life to bury her brother who was already dead, Antigone decides that the risk of being cursed in life and then being possibly rejected by the gods upon her death is a more dangerous risk. For these reasons she chooses to disobey Creon's command not to bury Polyneices, although her sister Ismene does not assist in the burial.

I've included a link to the study guide on Antigone.