In Beowulf, how does culture contribute to the creation of a hero?

One of the basic ways in which culture can be considered a creator of a hero is by manifestation. Lines 175–179 describe the people as worshipping at shrines and “vow[ing] offerings” (lines 175–176) in hopes that a “killer of souls” (line 177) will come to help them. It is not made clear how long the people did this, but the reader is aware of at least 12 years passing between the fall of Heorot to Grendel and the arrival of Beowulf. In a time before the internet, news traveled much, much slower, and therefore Beowulf in Geatland was not aware of this trouble for some time.
A more complex way in which culture contributes to the creation of a hero is through the specific focus of warrior culture. Beowulf essentially comes ashore and tells the watchman that he and his men are there because he can help Hrothgar defeat Grendel. When Hrothgar and Beowulf meet face-to-face the first time, Hrothgar tells him he has heard tales of him and his “strength of thirty in the grip of each hand” (lines 380–381). During the time that this story takes place, strength and tales of heroes were valued. Think along the lines of how the Greeks would have felt about Hercules and Odysseus. Beowulf appears to be heavily influenced by Germanic heroic poetry, which showed the relationship between a warrior and the lord he served. This shows not only the behavior of the characters within the story but also outside forces such as focus on heroes and strength in reality.
Another way is through obligation. Though it is admittedly difficult to keep track of who’s a distant relative, who’s a herald, and who’s an enemy, there was a long standing friendship between Hrothgar and Beowulf’s father, and this is partially why Beowulf feels a sense of duty to the king. This would have been a value taught to him from an early age. Then we have Grendel’s mother, who seeks revenge for her son’s death and takes back their “trophy” (line 1302) of his severed arm. Part of being a warrior, other than battle skill, was seeking trophies and being rewarded by your lord, which goes back to the Germanic heroic poetry influence.
All quoted material in this answer comes from the Norton Anthology of English Literature, The Major Authors, 9th Ed.