Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

If you want to call C from Perl, start with the perlxstut manpage, moving on to the perlxs manpage, the xsubpp manpage, and the perlguts manpage. If you want to call Perl from C, then read the perlembed manpage, the perlcall manpage, and the perlguts manpage. Don't forget that you can learn a lot from looking at how the authors of existing extension modules wrote their code and solved their problems.