These are the lines that are found toward the end of the poem. Beowulf is already dead - he has defeated the dragon, but has also died in the process. Before his death, he instructed his men to build a tower in his honor, so this part of the poem talks about that. It talks about how the Geats made this monument for their late king, and how they grieved his death by telling his greatest accomplishments, like defeating Grendel and his mother. Then they hid the dragon's treasures in the tower, as per Beowulf's instructions, so that no one could ever find them.
