Lodovico had just given Othello the letter that he was sent to Cyprus to deliver. He was upset that Desdemona was not understanding why he was mad and he ranted about people in relationships being unfaithful.
Iago turned on Roderigo and stabbed him and is now dead. Iago then attacks Cassio from behind and severely injures his legs. Cassio does not know who his attacker was so Iago was still in the clear.
Othello had killed Desdemona, Iago had killed Emilia in cold blood, and was detained. Othello then took his own life because of the misery that he put himself in by wrongfully killing his wife. Lodovico then appointed Cassio to be the Governor of Cyprus and Othello's assets and estate.