Bilbo saves the dwaves from the spiders in chapter ...8 i think..its called "FLies and Spiders" and bilbo also saves the dwarves in Chapter 9 from the woodelves....and bilbosaves the men and everyone else from smaug by finding out smaugs weakness(left brest)....in chapter 12
Chapter 8 shows Bilbo battling and winning the fight against the spiders. Chapter 13 is where Bilbo matches wits with the dragon and uses the ring to disguise himself. The last chapter (19) shows Bilbo coming home and they have presumed him dead and are auctioning off his things. Eventhough he puts a stop to it, the community never really accepts him as one of them. The act of heroism, here, then, is that he has the courage to continue to live in a group where he is not truly wanted, but is very much needed.