How are major plot elements revealed in "Medea?"
Many of the salient elements of the plot of "Medea" are revealed indirectly. First, one can assume that most of the original audience would have been familiar with the entire story before seeing the play as it was taken from a well known myth; thus less explanation would have been required for an ancient audience than you might need as a reader. The unities of action, time, and place require that the backstory be recounted indirectly and the action as it appears onstage somewhat compressed.
The devices used by Euripides to reveal actions not seen in detail on stage include prophecy, messengers, the nurse, and the chorus, all of whom at times report on actions not seen by the audience, as does Medea herself.