I haven't seen a guide on the forums about BBCode so I decided to make one.

To access a list of options for BBCode, click the button that looks like this:

Acronyms - Allow you to put an acronym and add a description to it.

Example: lol this feature is cool

Admin - Allows you to post content in a post that is only viewable by admins.

Example:

 

This content is only available to admins

Code:

[admin] (Content here) [/admin]

Background Color - Changes the background color of your text.

Example - what's up bishes

Code -

[background='(insert color here)'] (Text here) [/background] 

Blog Entry Link - Allows you to easily link other's blog posts.

Example - Battle for the net

Code -

[entry='(Entry ID)'] (Link Name) [/entry]

Blog Link - Allows you to link other's blogs.

Example - JHnY HaYZ's Blog

Code -

[blog='(Blog ID)'](Link Name)[/blog]

Code - Allows you to place code without accidentally using BBCode.

Example -

// As you can see, I can put [spoiler='hey']hey again[/spoiler] tags
// without the code actually fuctioning!

CollegeHumor - Allows you to embed CollegeHumor videos

Example -

Not gonna bother with giving the code since to my knowledge this BBCode is broken.

Extract Blog Entry - This allows people posting to their blogs to customize what shows in RSS feeds.

I can't provide an example, but basically if you have something that shows you your blog's RSS feeds, use this BBCode to customize what part of the post is shown in the feed. I am not sure if this is required for it to work with the RSS feed, though.

Code -

 [extract]Jxhn's BBCode Guide[/extract] 

Facebook Like - Allows people to like stuff on Facebook (Just HG it seems)

Example - Like this status I made on Facebook!

Seems to only work with HG's FB page or maybe just not with statuses.

Code -

[LIKE](Link to Facebook Page)[/LIKE]

Horizontal Rule - Adds a horizontal rule, as it says.

Code -

 [hr] 

HTML Code - Allows you to enter HTML code.

No example because I don't know HTML

Code -

[html](Code goes here)[/html]

Justin.tv - Twitch replacement

No example because I probably shouldn't embed a random cartoon on HG

Code -

[twitch](Link to the video/stream here)[/twitch]

Not sure if this is for a seperate website or twitch actually...

Media - Allows users to post media such as flash related stuff from lots of websites.

No example.

Code -

[media='(Dimensions go here if it is in flash)'](URL to the media here)[/media]

Member - Quick link to a member on this website!

Example -

Code -

[member='(Member name here)']

Multi-Page Articles - Allow users to make post that have multiple pages! (Broken)

No example so I don't mess up this long post.

Code -

To my knowledge, you can put this code anywhere you want to create a page break (will generate buttons to navigate between pages)

Ninja - Hides text until you click a button.

Example -

Code -

[ninja](Text to be masked)[/ninja]

PHP Code - Allows you to enter PHP code on a post.

No example since I don't know PHP.

Code -

[php](PHP Code goes here)[/php]

Post Link - A link to any post on this site!

Example - Current CS:GO moderators

Code -

[post='(Post ID here)'](Title of the link)[/post]

Spoiler - Allows you to click a button before viewing parts of a post.

Example - [spoiler=It's everyday bro]With the Disney channel flowExample - [spoiler=It's everyday bro]With the Disney channel flowExample - [spoiler=It's everyday bro]With the Disney channel flow

Code -

[spoiler='(Title for the spoiler, optional)'](Text to be masked)[/spoiler]

SQL Code - Allows you to enter SQL code on a post.

Example -

UPDATE bans SET approved = 'true', duration = '0', locked = 'true' WHERE steamid ="1:108614469'

Code -

[sql](SQL Code Here)[/sql]

Steam Profile - Allows you to show a Steam profile on a post

Example -

Code -

[steamprofile](Steam ID here)[/steamprofile]

Topic Link - Allows you to create links to topics on HG forums!

Example - How'd You Come Across HG?

Code -

[topic='(Topic ID here)'](Title for the link here)[/topic]

Twitter - A way to plug your Twitter on HG!

Example - @ExpertGamerJohn

Code -

[twitter](Twitter username here)[/twitter]

Username - A link to a user's profile

Example - Jxhn

Code -

[user](User's display name here)[user]

XML Code - Allows you to put XML code on a post.

No example since I don't know XML.

Code -

[xml](XML Code here)[/xml]

Credits:

SQL Example contributed by Pyrrhic

XML Example contributed by Pyrrhic

HTML Example contributed by Pyrrhic

PHP Example contributed by imasonaz

Source: Bbcode Guide