It can be confusing sometimes knowing where to look for documentation when dealing with C †
† that is if you're not a systems engineer, and have no CS degree, nor learnt C
As an example, you might learn about the strace command and start investigating what your Ruby application is up to. In doing so you'll see lots of calls to different functions and you might decide you want to look up the documentation for those functions.
This could be where your first problem arises. You might think "Ruby is written in C, so I'll look at the C documentation" and then come up with nothing.