Prologue: This is the introductory scene to a play. Usually it involves a limited number of characters that explain the necessary history to understand the current drama. In Medea this would be the scene between the Nurse ("O how I wish that ship the Argo/had never sailed off to the land of Colchis"), the Tutor ("Old slave from my mistress’ household,/why are you here, standing by the gate"), and Medea herself ("I can’t stand this pain, this misery./What do I do? I wish I could die!"). 

Parados: The first song spoken or sung by the chorus. This scene begins in Medea when the Chorus Leader comes on. 

First Episode: In an episode, characters and chorus members talk and advance the plot. It's important to remember that in Greek theatre no more than 2 or 3 characters can be onstage (besides the chorus, who weren't really onstage at all but in a separate place called the 'orchestra').

Choral Ode: A song or chant performed by the chorus. Usually this would be combined with a dance or ritual of some kind. 

Second Episode: The second scene between characters. 

Choral Ode: The second choral ode. 

(...) The rest of the play should go back and forth between episodes and choral odes. 

Exodus: Finally, at the end of the play, the chorus gives some piece of final wisdom. Here is the exodus from Medea:

      "Zeus on Olympus,
      dispenses many things.     
      Gods often contradict
      our fondest expectations.
      What we anticipate
      does not come to pass.
      What we don’t expect
      some god finds a way                                                           
      to make it happen.
      So with this story."