Finding docs for #include Directives

[over9k]

I'm poking around in some source of applications, and realized that I need more information on the includes to better understand what is going on.
i.e.:

#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>
#include <unistd.h> 

Where can I find this information, some of these aren't in the reference here.
Thanks.

[firedraco]

I would try checking the man pages first.