Death Hallows are 3 magic and powerful objects created by the Death. It contains the Elder Wand, the Magic Stone and the Cloak of Invisibility. Harry already had the Cloak of Invisibility which was given by his parents and he also knew where were the other 2 objects. Voldemort has came alive and controlled the world of wizard, so Harry has to defeat him and protect his friends and families. Harry has to get the Elder Wand and the Resurrection Stone. With all 3 things together, Harry will be as powerful and mighty as the Death. However, the story of the Three Brothers is a household story, so Voldemort must know it too. Therefore, what Harry is going to do is to find the Deathly Hallows first and use them to kill Voldemort for good.
Of course, Harry will encounter plenty of difficulties and setbacks, but he has friends, especially Ron and Hermione. The two of his best friends will help him till the end of the world. Moreover, Harry is the descendant of third brother which means he will survive eventually, as well as his friends. I believe, in the end, Harry will defeat the "undefeatable" Voldemort.