Messages in the forum can be formatted with tags similar to HTML, HTML is not available in the forum. Often known as VB tags I call them pseudo tags. Here your find the overview of possible pseudo tags:

Format	Pseudo tag	HTML counterpart	Examle/Explanation	Display
Bold letters	[b]...[/b]	<b>...</b>	[b]These are bold letters.[/b]	These are bold letters.
Italic	[i]...[/i]	<i>...</i>	[i]These are italic letters.[/i]	These are italic letters.
Underlined	[u]...[/u]	<u>...</u>	[u]This is underlined.[/u]	This is underlined.
Center text	[center]...[/center]	<center>...</center>
Justified text	[justify]...[/justify]	<p align=justify>...</p>
Left aligned text	[left]...[/left]	<div align=left>...</div>
Right aligned text	[right]...[/right]	<div align=right>...</right>
Superscript	[sup]...[/sup]	<sup>...</sup>	normal [sup]superscript[/sup] normal	normal superscript normal
Subscript	[sub]...[/sub]	<sub>...</sub>	normal [sub]subscript[/sub] normal	normal subscript normal
Font size 4	[size+4]...[/size]	<font size=+4>...</font>	[size+4]four[/size]	four
Font size 3	[size+3]...[/size]	<font size=+3>...</font>	[size+3]three[/size]	three
Font size 2	[size+2]...[/size]	<font size=+2>...</font>	[size+2]two[/size]	two
Font size 1	[size+1]...[/size]	<font size=+1>...</font>	[size+1]one[/size]	one
Font size -1	[size+1]...[/size]	<font size=-1>...</font>	[size+1]-one[/size]	-one
Font size -2	[size-2]...[/size]	<font size=-2>...</font>	[size-2]-two[/size]	-two
Font face	[face=Schriftart]...[/face]	<font face=Font face<>...</font>	[face=courier]courier[/face]	courier
Link	[url]...[/url]	<a href="..." target=_blank>...</a>	[url]http://forum.sheila-heiko.de/[/url]	http://forum.sheila-heiko.de/
Link	[url=Link]...[/url]	<a href="Link" target=_blank>...</a>	[url=http://forum.sheila-heiko.de/]PHP-Forum[/url]	PHP-Forum
Email address	[email]...[/email]	<a href="mailto:">...</a>	[email]john.doe@does-not-exist.invalid[/email]	john.doe@does-not-exist.invalid
Email address	[email=Addi]...[/email]	<a href="mailto:">...</a>	[email=john.doe@does-not-exist.invalid]Mail to John Doe[/email]	Mail to John Doe
image	[img]...[/img]	<img src="http://forum.sheila-heiko.de/forum/graphics/new.gif" border=0>	[img]http://forum.sheila-heiko.de/forum/graphics/new.gif[/img]
Enumeration list	[ul]...[/ul]	<ul>...</ul>
Enumeration list	[ol]...[/ol]	<ol>...</ol>
Enumeration list - 1, 2, 3...	[ol=1]...[/ol]	<ol type=1>...</ol>
Enumeration list - i, ii, iii...	[ol=i]...[/ol]	<ol type=i>...</ol>
Enumeration list - I, II, III...	[ol=I]...[/ol]	<ol type=I>...</ol>
Enumeration list - a, b, c...	[ol=a]...[/ol]	<ol type=a>...</ol>
Enumeration list - A, B, C...	[ol=A]...[/ol]	<ol type=A>...</ol>
Line in enumaration list	[li]...[/li]	<li>...</li>
Table	[table]...[/table]	<table>...</table>
Tabelle with border 1-5	[table=n]...[/table]	<table border=n-5>...</table>	n=1, 2, 3, 4, 5
Table row	[tr]...[/tr]	<tr>...</tr>
Table cell	[td]...[/td]	<td>...</td>
Table cell vertical alignment top	[td top]...[/td]	<td valign=top>...</td>
Table cell vertical alignment bottom	[td bottom]...[/td]	<td valign=bottom>...</td>
Table cell vertical alignment middle	[td center]...[/td]	<td valign=center>...</td>
Head lines 1-4	[hn]...[/hn]	<hn>...</hn>	n=1, 2, 3, 4
Font colors	[farbe]...[/farbe]	<font color=COL>...</font>	für "COL" eines der folgenden farbworte setzen	black maroon green olive navy purple teal silver gray red lime yellow blue fuchsia aqua white
Font colors	[color=xy]...[/color]	<font color=xy>...</font>		For xy use one of the color words above or RGB values in hex format, for example #ff0000 for red.

Note: All tags must be written as shown here which means no blanks or capital letters are allowed.

There is also the pseudo tag [br] for the HTML line break <br>. If [br] is uses once or more in a text, line breaks will only be done on the [br] tag. If [br] is not used in a message at all, a line break will be set at every place where "Enter" was inserted in the message. You not have the need of [br] in most cases but it may help if you use tables or enumarations. Using [br]in this cases will help you to keep overview of all the [tr], [td] and [li] tags by using "Enter" without becomming all these "Enters" a line break in your messages.