My responses so far have assumed you wrote the original code. Your subsequent replies seem to suggest this is not the case. There is a lot of very basic code that you do not appear to understand.

That's all fine. Before I saw any Perl code (20+ years ago), I didn't know any of this either. However, you do need a basic foundation before anything more advanced is likely to make much sense.

I strongly recommend you read "perlintro -- a brief introduction and overview of Perl". This will explain much of the beginner concepts; and it provides links to more detailed information for topics introduced. It's not a particularly long document and I suggest you read it in full: it should bring some clarity to the advice you've been given (by myself and others) in this thread.