How does どうするんだ function here? For more context, see the full text here: < Taken from line 3: **** ... On jisho, translates into "what to do about it" < I feel rather unsure about the implementation of this meaning here. I'd translate the sentence like this: "Hereupon, one of the men bragged: "Such things, being afraid what to do about it?..." I think this phrase goes in the direction of "Such things, why bother with being afraid?" or "such things, what do you do about feeling afraid". The latter would imply a question about what they do to cope with it. I would say that the first of the two interpretations is probably more fitting here, but as I said, I don't really know what to do with this here.

The guy is basically bragging that he is not scared of that "thing", and in a way mock everyone who is scared.

The might not be easy to understand. It technically means,

> "what you gonna do about it",

but the meaning is more something like,

> "how can you keep on going(living your life etc...) if you can't handle this".
> "What are you gonna do if you can't even handle that".
> "If you can't manage that much, there is nothing you can do(you are doomed to failure/mediocrity)"

Another easy way to understand might be to see it like this.

> Oh no what shall we do!