After Prometheus steals fire from Zeus, and Zeus chains him to a rock, the king of the gods has a plan. He begins to create the "gift" he wants to give to the mortals with Hephaestus help.
Damn that Prometheus for taking my fire, Hephaestus make me a woman
After Hephaestus completes the woman, Zeus names her Pandora.
Zeus tells Pandora how she is going to be a gift to Epimethius, Prometheus's brother, and she will marry him. He then gives the woman a small box. Zeus tells her to never open it.
Now Pandora listen, you will never open this box. Is that Understood?
Zeus brings Pandora to Epimethius, he tell him to marry Pandora and to never open the box. He gives Epimethius the key to the box and tells him to hide it. Epimethius accepts his "gift" and Pandora is now his wife.
Even though Zeus told Pandora she wasn't allowed to open the box, Pandora's curiosity would burn like a flame in her. She would always ask for Epimethius to let her open the box, but the man refused her demands.
One night, Pandora couldn't take it anymore. Her infatuating curiosity got the best of her, she grabbed the box and key from the hiding spot her husband tried to hide them in, and quietly left the house.