Does your school refuse to let you access a some site while in class? Is Facebook blocked, and you desperately need to unblock it? You need to go to Facebook, but the school has it blocked? Then carry on reading.
Unblockers are like a gateway that pass information between your computer and the site you're trying to visit. The unblocker accesses the site on your behalf, accesses the page, and forwards it to you. So the site you want to be on never sees your IP. So actually you are visiting websites in an indirect way. School firewalls think you are just visiting the unblocker, not the real site.
Another way of unblocking Facebook at school is by setting up your own unblocker tool. This is more advanced than just using an unblocker but it pays off because if they block it, you can make another. How to do this is not in this guide, do a search for "How to make your own proxy" you should find help. You can even make money from letting people use it by letting people advertise on it.
Some other ways to unblock Facebook include by using sites that translate pages, for example Google Translate or Babelfish. You can also try using Google's cache copy of the site. Although, it won't let you to log in that way, so it's still better to use an unblocker for Facebook, however these tricks work with many other sites.