Linux, C++ and the extern "C" keyword

I am reading a book on C++ and I have a question on how some of it might
apply in the case of Linux. I believe the author of the book('Practical C++'
by Rob McGregor) bases all of his work and examples on the Windows platform,
though it isn't a windows-specific book.

I also have another book that serves as an introduction to Linux
programming, with all of the examples being done in C. The book describes of
the many C-specific function calls that are available for the Linux
platform.

My question is, if I wanted to write an application on Linux using these
C-specific function calls, would I have to do anything with "extern 'C'" for
the function calls, or would I be able to just #include the appropriate
header files and rock out from there?

Thanks
Lucas Vogel