Another thing that really helped me was to locate where the CPAN library modules on your system are located, open up a (read-only!) editor or browser, and skim through the code. I prefer to learn by example. (And the operative word here is skim. You won’t understand everything you have seen, but you will have seen it.) I think that this will be an important adjunct to the books, perldoc topics and other sources previously mentioned.
You can find the locations by entering perl -V with an upper-case “V” and looking through the (rather voluminous) output.