Basic instructions
Using the URL Shortener
Simply type (or copy/paste from your browser's address bar) the URL which you'd like to make smaller into the text box on the main page. Push the "Compress That Address!" button, and pxlz.org will make the address smaller for you, and give you a new link. You can then copy this new URL wherever you'd like to use it.
To use an address shortened by pxlz.org
There is no need to visit pxlz.org to use a shortened address. Simply type or paste the shortened URL into your browser's address bar and press enter, you will be automatically forwarded to the original address. If somebody has given you an pxlz.org URL in the form of a hyperlink, just click on the link instead.
Additional functionality
How to preview an pxlz.org shortened address
It's very easy to find out where any pxlz.org shortened address will take you without having to visit it. This is useful to check that the link will redirect to a destination you trust. Simply add a hyphen (dash) to the end of the shortened URL, and instead of being redirected to the original long address automatically, you'll be taken to a preview page telling you where the link goes.
For example: You have been given the shortened link http://pxlz.org/1 and want to check where it goes. Copy/paste it into your browser's address bar and then add a hyphen, making the link http://pxlz.org/1-. Now simply visit that address, and instead of being taken directly to the original URL, you'll be taken to a preview page on the pxlz.org site which will tell you the link's destination.
Bookmarklet
If you need to use pxlz.org frequently, you can bookmark this 'magic' link: Pixelize with pxlz.org!. Visiting the bookmark will then create a shortened URL for the site you are currently visiting, without you having to visit pxlz.org. This functionality requires Javascript to be turned on in your browser (usually on by default), and you can safely ignore any security warnings that pop up when adding the bookmark, these are because the link contains Javascript code.
Additional keywords
Everything after the tailing "/" in a shortened URL is ignored, so if you'd like additional keywords or "hints" to a URL, you can take advantage of this to manually add them. For example, if I created the shortened URL http://pxlz.org/4 that redirected to an IT news site, and wanted to add additional keywords to the link, I could give it out as http://pxlz.org/4/itnews or even http://pxlz.org/4/news-site/for/nerds. Everything following the / after the 4 is ignored, so they are all equivalent.