At school, you're forever being told what to do. Your parents tell you to go, the school staff tell you what to think, what to eat, what to wear, who to hang out with (and who not to)... the list goes on. It's a lot like prison, apart from the fact that you did nothing wrong. You'd guess that since you're forced to go to class and all that stuff, they would at the very least let you browse whichever web sites you want while you're there. Apparently not. The interwebs are censored, a good deal of web sites are being blocked. Luckily, there are a few ways to get past the restrictions at least, and it's very much more easy than convincing your parents to homeschool you.
An unblocker is like a gateway that pass information between your computer and the site you're trying to visit. The unblocker accesses the site you want instead of you, accesses the page, and sends it off to you. So the site you want to access only sees the unblocker's IP. So, basically you are browsing sites in an indirect way. School firewalls only think you are accessing the unblocker, not the real site.
An alternative way to unblock Facebook at school is to set up your own unblocker tool. This is harder than using someone else's unblocker but better in the long run because you're in control. Explaining how to do this is not in this guide, do a search for "How to make your own proxy" you will find info. You can also make money from your unblocker if you put ads on it.
Other ways to get on Facebook are to use sites that translate pages, for example Google Translate or Babelfish. You can also try using Google's cache copy of the site. However, it won't let you to login using these methods, so you're better off using unblockers for Facebook, though these tips work with many other sites.