Final answer:
Beowulf boasts of several heroic deeds, such as his victorious swimming match against Breca while fighting sea monsters, and his combat prowess proven by defeating many beasts and giants, to establish his reputation as a formidable warrior.
Step-by-step explanation:
Beowulf's boasts are a key element in understanding his character and the values of the society depicted in the epic poem. They serve as an insight into his past heroic deeds and establish his credibility as a warrior capable of facing the threats that the poem's setting presents. Some of Beowulf's boasts include his swimming match against Breca, where he not only outswam his opponent but also fought off sea monsters.
Additionally, he boasted of his strength and skill in combat, which he had proven by fighting and defeating many beasts and giants. Interestingly, these feats are reflective of an honor-bound society where one's reputation is paramount, and storytelling serves as both entertainment and a historical record.