It was sung - as with most songs you can probably get the drift without understanding all the words in full detail. However these notes might help!
(l.45) War has been going on for 10 years (and still is as far as we know)
Agamemnon & Menelaus, sons of Atreus, joint kings of Argos, led a huge army off on a rescue mission.
(55) They were like vultures robbed of nestlings: angry, but helpless - unless gods intervene to punish the robbers.
(66) Gods did intervene to help Agamemnon & Menelaus punish Paris for taking Helen - because Paris, in taking her, violated the guest/host relationship (xenia). Zeus' most important job is to protect guests and hosts. Paris' punishment is inevitable.
(80) We (the chorus) are very old men - too old to fight 10 years ago. They have little time
(92) Why is the queen (Clytaemnestra, Agamemnon's wife) making sacrifices at all the altars in Argos? Some disaster?
(112) We remember when the army left - the terrible omen. Two eagles tore open a pregnant hare in full view of all.
(126) Calchas the seer explained it: Agamemnon & Menelaus will take Troy, but anger Artemis, the goddess who protects all innocent creatures (including the victims when Troy is sacked).
(140) She will stop the fleet sailing unless there is a sacrifice...
(150) ...the mother of the innocent victim is waiting for revenge...
(161) We don't understand the gods - but we believe Zeus has a rule: it is through suffering that men learn (i.e. there is a good purpose behind all this horror). From the gods comes "violent love". They hurt us, but for our good in the end.
pathos = mathos: suffering = learning)
(185) The army, becalmed at Aulis, was falling apart through hunger and boredom. Calchas told Agamemnon that Artemis would stop the winds until he sacrificed his daughter Iphigeneia.
(205) Agamemnon is trapped: if he doesn't kill Iphigeneia, then he will anger Zeus. If he does, he will anger Artemis and his wife. Whatever he does will be right AND wrong.
(216) He decided to kill her - they slaughtered her like an animal ignoring her innocence, her beauty and her screams.
(247) We don't know what will happen next.