Moth asks the Dragonborn to obtain Daedra heart for him. These can be obtained from the Daedra at the Shrine of Mehrunes Dagon, bought from Enthir at the College of Winterhold or bought from Babette. For all locations to obtain a heart, see here.
When the heart has been obtained and brought back to Moth, he'll reward the Dragonborn with a random piece of leveled armor. He will also allow access to the Orc Strongholds, if not already acquired. Moth also becomes a candidate for marriage after the quest is finished.