Assuming you already have experience with object-oriented programming in other languages, this page should help out. Books were very helpful for getting me started on Perl, but I think (at least for me) it can also be beneficial to look things up online as I need them and find examples.

However, if you do not have any prior experience with object-oriented coding, I would then definitely suggest hitting the books first. I'm sure all the suggestions on this thread are a good place to start. You can also look through the review section of this site to find more books.