It can be hard to know where to start. I tend to learn by experimentation and osmosis. I spent most of a year writing tiny little experimental programs and changing them, just to see what happened.

Sometimes it helps to browse through perlfunc, just to see what built-ins Perl has and perlfaq, just to see the common questions. It also helped me a great deal to read through all of the questions on Perl Monks and their answers (as well as comp.lang.perl.misc, in those days), to get a feel for what kind of answers there were.

One good trick, if you have time, is to take a question you think you might possibly be able to answer, then write a little code to come up with the answer or test your answer. You don't have to respond, but you can check your work against the answers of people who do respond.

Those approaches don't always give you answers to specific multipart questions, but they do often give you answers to pieces. If you know how to process files and if you know how to find file dates, all that's left is putting them together. Sometimes that's difficult, but writing a little glue is often easier than doing the whole thing yourself.