What does orsino ask viola to do in Twelfth Night?

In Twelfth Night by William Shakespeare, Orsino asks Viola, disguised as a young man named Cesario, to deliver a love letter and speak to the Countess Olivia on his behalf. Orsino is in love with Olivia, but she has been mourning her brother's death and has vowed to remain unmarried for seven years. Orsino hopes that by sending Viola to speak to Olivia, he can convince her to change her mind. Viola agrees to help Orsino and sets off to find Olivia.