BB stands for "Bulletin Board". It has two benefits:
Most BBCode consists of an opening tag and a closing tag, with the text you want to format going in between. If your BBCode isn't working, be sure to check that you've remembered to close your tags.
An opening tag might look like this: [b]
Closing tags generally look just like the opening tag, but with a slash, like this: [/b]
To bold, use [b][/b] tags.
To italicize, use [i][/i] tags.
To underline, use [u][/u] tags.
To strikeout, use [s][/s] tags.
To change the size of your text, use a [size=x][/size] tag. Just pick a number between 0 and 7 to represent the size you want and put it in place of the x, with 0 being the smallest and 7 being the largest.
To change your text color, use the [color=blah]...[/color] tag. You can either enter a color name, or a HEX code.
There are five tags you can use to align your text. [left][/left], [right][/right], [center][/center], [justify][/justify] and [indent][/indent]. Indent adds about a half-inch margin to the left side, useful if you want to set something apart from the rest of your text, like a quote or some song lyrics.
To add an image, use the [img]your picture url here[/img] tag.

If you want to let text wrap around your images, you can use the align parameter to move the image to the left or right like so:
Here is a bunch of text that is going to wrap around my image. I can create lots of great effects on my character profile with this simple technique. In this example, I moved the image to the left of the text, but I could just as easily have moved the image to the right. The difference between this command and the [right][/right] and [left][/left] alignment tags that are shown above is that in those cases, the thing inside the tags will be moved to the correct location, but they won't necessarily cause text (or anything else) to move up to occupy the new empty space that was created. The only way to be sure that your image will make room for other things on the same line is to use this special alignment property in conjunction with the image tag.Be warned: More things may wrap around your image than you originally bargained for!
To place a link, surround the text that you want to be clickable with the [url=][/url] tags, with the = pointing to the URL where you want the link to go.
There are several types of list possible with BBcode. The simplest uses the [list][/list] tags, with each point in the list preceded by a [*] tag.
Alternatively, if you would like a numbered list, use [list=1][/list]
If you would like to embed a youtube video into your profile, you need only use the [youtube][/youtube] tags. What goes inside the tags is the video ID.
Most youtube videos have URLs that look something like this: http://www.youtube.com/watch?v=xMrN3Rh55uM That garble of numbers and letters is the video ID, and what you want to put inside the tags.
If you want to make the video bigger or smaller, you may also include a width and height, like so:
[youtube width=640 height=385]xMrN3Rh55uM[/youtube]
If you would like to embed a vimeo video into your profile, use the [vimeo][/vimeo] tags. What goes inside the tags is the video ID.
Most vimeo videos have URLs that look something like this: http://vimeo.com/10351634 Those numbers are the video ID, and what you want to put inside the tags.
If you want to make the video bigger or smaller, you may also include a width and height, like so:
[vimeo width=400 height=225]29189421[/vimeo]
If you want to talk about the end of a movie but don't want to spoil it for those who haven't seen it, the [spoiler][/spoiler] tag is a good way to go. It will blot out the offending text, so that it has to be highlighted to be read. That way, people can choose whether they want to know the end of the movie in advance or not.
This is a great option, because it will work even for people who have disabled javascript.
[collapse][/collapse] is a fancy, interactive tag! As the title implies, it will condense a large amount of information into a very small space, and through the use of javascript, reveal it when the title is clicked.