You can read this book from cover to cover if you like, but for the most part each hack stands on its own. So feel free to browse, flipping around to whatever sections interest you most.
If you're a Perl "newbie," you might want to try some of the easier hacks (earlier in the book) and then tackle the more extensive ones as you get more confident. If you want more information on Perl, such as the background and documentation not found in this book, see perl.oreilly.com. Likewise, go to scripting.oreilly.com for more information on JavaScript, and check out web.oreilly.com for help with HTML.