Can you deliver this message to Lady Olivia for me?
Act 1, Scene 5
Malvolio! Go after Cesario and give him this ring!
Cesario (Viola in disguise) becomes one of Orsino's favourite in only a few days. He trusts him with his most important errand, which is to deliver his love letters to Olivia. Orsino thinks that Olivia will be impressed because Cesario is a young, handsome man. The audience learns that Viola is in love with Duke Orsino, so she reluctantly agrees to deliver the letters.
Cesario comes to the house of Olivia to deliver Duke Orsino's letter and acts as though he adores Olivia, which is what Orsino told him to do. Olivia falls in love with Cesario and sends Malvolio after him with a ring that she pretended Cesario left for her.