Try searching Tags for things like "bgg", "reference", "post_formatting", "bgg-reference", etc.
Note that if you see a forum post that has the effect you want, you can simply click the Quote button to see the source code of how that post did it. Then simply go back in your browser or close that tab or window, instead of actually posting a meaningless reply.
The rest of this document explains the various format codes for forum posts.
Beware that the < bug can delete most of your post!
Sometimes users unknowingly use the symbol < in their posts with text immediately after it (with no space). The forum software too aggressively strips out all the following text, i.e. the rest of the post, to protect against possibly malicious HTML code. If you really need to make the symbol < appear with a non-space character immediately after it, try using & lt; (remove the space between & and lt;) to create < in your post... This problem has been known for a long time, but still hasn't been fixed. http://www.boardgamegeek.com/thread/601039/less-than-character-in-review-doesnt-work http://boardgamegeek.com/article/6731442#6731442
Format codes without buttons to create them
[ microbadge = # ] (replace # by the number of the badge and remove the spaces) will cause the image of the given microbadge to appear in the post, with a link to its page and hovering description when mousing over the image. The number can be found in the URL of the microbadge.
[ floatleft ] image [ /floatleft ]
[ floatright ] image [ /floatright ]
These make an image (and possibly other stuff) float left or float right within the body of the text. See this thread for examples and more discussion.
[ center ] image [ /center ] centers whatever is within the "center" block
[ clear ] resets the display location (after the use of float left, float right, or center) so that new items or text are not laterally affected by earlier items.
Forum comment buttons to help with format codes
Note that when typing a forum post, there are many useful buttons above the text field. These include:
= create [b][/b] around selected text (bold) = create [i][/i] around selected text (italic) = create [u][/u] around selected text (underlined) = create [-][/-] around selected text (strikethrough) = create [COLOR=#xxxxxx][/COLOR] to change the foreground (text) color = create [BGCOLOR=#xxxxxx][/BGCOLOR] to change the background color = create [ ImageID=xxxxxx] to display an image hosted at BGG.
Note that with ImageID you can give an optional argument (micro, square, small, medium, large, original) in the brackets to set the image size, e.g. [ ImageID=xxxxxx original]. The default is small. See this thread by Aldie. = create [IMG]http://foo.bar/com.jpg[/IMG] to display an arbitrary image at any URL.
Note that there is also [INLINEIMG]http://foo.bar/com.jpg[/INLINEIMG] to display an image in the line of text instead of putting it on its own line. = insert a poll = insert a quiz = insert a Youtube video id. To start the video at a specific point, add "&start=" and the offset in seconds (e.g., "&start=66" will start the video at 1:06). = insert a Vimeo id = insert an mp3 (via its URL) Game button = create [GAMEID=xxxxx] to display game title that's a link to the game's article. The game number xxxxx can be found in the URL of the game page. Quote button = create [q][/q] to display quoted text. You can edit the first part to be [q="user name"] Spoiler button = create [o][/o] to make a text boxes that hides its text until the user mouses over it to reveal the "spoiler" text. Useful for discussing movie surprises, quiz results, etc. Code button = create [c][/c] to make a block of text print in fixed-width font with no automatic formatting. Useful for showing program source code, simple tables and charts, ASCII art, etc. URL button = create [url][/url] to make a pretty link to a URL. E.g. [url=http://google.com]Google[/url]. WIKI button = create [wikipage=abcde] to make a link to the wiki page about abcde. Note you can also do this easily by putting double square brackets around abcde like [ [abcde] ] this (but without the spaces, resulting in abcde) - the double bracket notation that works in the wiki itself also works in forum posts to make a link to a wiki page. Font size pulldown = create [size=xx][/size] to change the display size of selected text
Note that the Game button's functionality has an annoying problem that it shows about the first 50 titles that have the search text anywhere in the title. So looking for a game like "Set" or "Nim" fails, and you must open a separate tab/window to use the main BGG game search (which more conveniently shows games that start with the search string first) to find such games and then copy the gameid to the forum post.
This is a reported bug: https://boardgamegeek.fogbugz.com/default.asp?213_jv0g
Examples of use of the forum format codes
Quoting with a username:
[q="SomeUser"]the quote goes here[/q].
[MP3]hVitttp://audio.cdbaby.com/9d939172/mp3lofi/a/n/angelnash-01.mp3|title[/MP3]
[GAMEID=237]
[o]spoiler text[/o]
[c]insert code here[/c]
[url=http://somesite/index.html]sometext here[/url]
[wikipage=forum formatting] tiny text small text normal text large text huge text
[ username=Aldie ] in a forum post will display the user's name, avatar, email link, etc
= create [b][/b] around selected text (bold)
= create [i][/i] around selected text (italic)
= create [u][/u] around selected text (underlined)
= create [-][/-] around selected text (strikethrough)
= create [COLOR=#xxxxxx][/COLOR] to change the foreground (text) color
= create [BGCOLOR=#xxxxxx][/BGCOLOR] to change the background color
= create [ ImageID=xxxxxx] to display an 
= create [IMG]
= insert a 
= insert a 
= insert a Youtube video id. To start the video at a specific point, add "&start=" and the offset in seconds (e.g., "&start=66" will start the video at 1:06).
= insert a Vimeo id
= insert an mp3 (via its URL)
