It was to give the audience pre-existing knowledge about the play that would help with the understanding of the play and its conflicts and often it foreshadows something that is going to happen... for example the begging of Romeo and Juliet when the chorus tells us that there is a feud between the two families and how it was a tragedy of star crossed lovers.
What? I dont understand the question in this ?
Answer: When he and his surviving men escape Polyphemus, Odysseus taunts the Cyclops, telling him his real name (he used a fake one before). Polyphemus (the cyclops) cries out to his father, Poseidon, who exacts revenge on Odysseus by keeping him lost at sea for many more years before finally allowing him to make it back to Ithaca and his son and wife.