Consider the myth a belief system. At some point the people who told and heard the story of Pandora's box likely believed that it was true. They also believed that it was important, or the legend would not have been repeated, written down and passed on to us today.
Think of the myth of Pandora's box as an effort to explain something about the world. In prescientific cultures, myths were frequently used to explain something that people could not otherwise know. When viewed as an origin myth, the story of Pandora's box explains the presence of evil in the world. According to the ancient Greeks' beliefs, evil exists because Pandora opened the box that Zeus gave her.
Examine the myth of Pandora's box as a fable that teaches a moral truth. Myths were often intended to instruct, and the myth of Pandora's box is no exception. In the story, bad things happen because Pandora yields to her curiosity and opens the strange box given to her by Zeus. If Pandora had resisted temptation and left the box alone, evil would not have escaped into the world. The moral of this story makes more sense if we know that the Greek culture of the time valued obedience rather than curiosity as a female virtue. That may be why Pandora's act of curiosity, though considered reasonable today, is so harshly punished in the myth.
Read the myth as a story. For all their historical significance and complicated narratives, myths are, at heart, just stories. They were meant to entertain their audiences. When interpreting a myth, you can use all of the techniques that you would use for any other type of literature to help reveal its meaning.