From what I can tell I need to start with open (XCACLS, "xcacls.txt") or die "Cant open file: $!\n"; But then I get stuck.

Okay, you're opening xcacls.txt for input. You can then read lines out of it with the <> operator, thusly:

You probably also want to open a file for output:

The best advice anyone has given you is to ditch the 21-Days book. The worst computer technical book I've ever read, and I've read some pretty lousy ones, was from that series (although it was the VB one, not the Perl one). In my experience, even "for Dummies" books are better than "... in 21 Days" books, but really you probably want to get an O'Reilly book, or use the online documentation, or both. Perlmonks is also a great resource, when you have specific questions or problems.

And yes, having a project to work on is a good way to learn a programming language. Each time you learn some new feature of the language, you can maybe apply it to your project, which gives you a feeling of progress. Extra bonus points if the project is a fun project, but any project at all is better than having nothing particular in mind.