But what I really want is to implement a code that makes it "almost" all the links from my site they see a shortener. But I want the links to appear shortened only in my forum and the homepage of my website.
Hmm...The thing is that i have never been into this type of type of url (shortener) before. So i have no clue how it works then what you told. But for me it sounds like this should be something in the settings of your account in the adf.ly site.
So you dont get an option where you add links that you want to get shortened or something. Or maybe contact their support. If not maybe the Admin for this site have heard about it before.