Eteocles and Polyneices have killed each other in battle.
Antigone and Ismene discuss Creon's decree that their brother Polyneices will not receive a proper burial and anyone who tries to bury him will be put to death.
Antigone informs Ismene she intends to defy the law and give Polyneices burial rights. Ismene talks her out of it. Antigone insults her.
After the death of Oedipus the King his sons Eteocles and Polyneices are to rule in alternating years.
Eteocles rules first but when his year is up he decides he likes being king and does not abdicate the throne.
Although Antigone likely recognises Creon's manipulation, she helps Polyneices because it is the rightthingtodo.
The fact that Antigone acts alone against the wishes of the king, against social customs that consider women inferior makes her even more heroic.