This obviously doesn't apply to all C code, but one thing that I like to do is to find some sort of endpoint. A piece of code that communicates with the "outsid

This obviously doesn't apply to all C code, but one thing that I like to do is to find some sort of endpoint. A piece of code that communicates with the "outside world" and start from there. See what commands you can send to the software and how they are the handled. This is often a good way to get into what the code does and how it does it.