IMHO, one of the best discussions of complex data structures, and how to access their innards, is to be found in Chapter 3. References and complex data structures of perlinter.pdf, available from Perl Training Australia. You'd probably want the most current version of the course notes, though, which have been reworked into progperl.pdf, available from the same page noted above.

You might also wish to take a look at:

intro to references
References quick reference

HTH,