I've literally just figured out how to do this, and it seems a lot of you guys were having trouble with it too -- so, tada, a guide!
Our profile layouts use what we call BBCode. If you've tried using it before to no avail, perhaps it was because you used quotes with your code, like I was doing...darn HTML xD
Anyway, read away!
★ 1. Text adjustments
Size
Ever wanted to make your text a specific size? You'll need to use this code:
PHP Code:
[size=1]text[/size]
Result:

Color
This is a lovely code which will allow you to change the colors of the text in your profile. You can use regular words such as red, green, blue etc, OR you can use hex codes. If you're unsure what hex codes are, feel free to drop me a message =]
PHP Code:
[color=red]text[/color]
Result:

Bold, Italic, Underline
A set of extremely simple codes -- and they make such a difference to your profile!
PHP Code:
[b]text[/b]
[i]text[/i]
[u]text[/u]
Result:

★ 2. Alignments
Center, Right, Left
These codes will align your text to the center, right, or left -- it can really help organize and tidy up your profile ^_^
* This code was being temperamental, so simply remove the # when you use it =]
PHP Code:
[center#]text[/center#]
[right]text[/right]
[left]text[/left]
Result:

★ 3. Links
To add a link to your profile, simply add the following. The url is the
website address, in case you didn't know.
PHP Code:
[url=url goes here]text[/url]
Result:
Unfortunately, the code to add images doesn't seem to be working ;___;
I hope this guide was of use to you! I'll tidy up the images sometime too. xD
There's a myriad of other codes you can use, but hopefully this covers the basics x) be sure to experiment if you have the time!