If you interested in perl5's internals even for a little then will find this article useful. It doesn't describe quite well described SVs, AVs, HVs and other representations of perl structures, but introduces on examples execution of a perl code.
I know a few things about internals, but author's point of view allowed me to understand better RETURN and PUSHBACK macros, stack pointer, op_tree.
It's one tiny step towards understanding how cool things, like Devel::NYTProf, work.