There are two ways to create these custom pages. One way requires making a PHP file, like mycustompage.php and making a template like MYCUSTOMPAGE. The other way is a bit simpler and just requires making a template.
There is a difference in how the pages will appear (based on what method you use). The harder way will make things look more "pretty" because it will have a URL that looks something like
http://www.Example.com/forums/lol.php
while the easier way will have a URL like
http://www.Example.com/forum/misc.php?do=page&template=lol
(lol being the example name of the page you are creating)
The harder method will be able to have a custom breadcrumb, and the easy one will have a breadcrumb that is basically the template name.
I only use the easier method, and this is how I do it:
Bring up the AdminCP and go to the Style Manager. For the style that you want to have the page in, click the options select bar (it says "All Style Options") and select "Add New Template" (and click go if the page doesn't automatically change).
Now you will be faced with two important boxes (the Title box and the Template box). For the title, you can have it whatever you want, but it must have "custom_" in front of it (for instance, custom_lolz). It should all be lowercase because everything after "custom_" will be within the URL, and every internet link should always be lowercase.
Now for the Template box, you should copy this code and paste it in there to begin with:
$stylevar[htmldoctype]
<html dir="$stylevar[textdirection]" lang="$stylevar[languagecode]">
<head>
<title>$vboptions[bbtitle]</title>
$headinclude
</head>
<body>
$header
$navbar
<table class="tborder" cellpadding="$stylevar[cellpadding]" cellspacing="$stylevar[cellspacing]" border="0" width="100%" align="center">
<tr>
<td class="tcat">%ARTICLE1_TITLE%</td>
</tr>
<tr>
<td class="alt1">
%ARTICLE1_CONTENT%
</td>
</tr>
</table>
$footer
</body>
</html>
You can have more than one article (with a title and content) on a custom page. To do that, just copy the code between the:
<table class="tborder" cellpadding="$stylevar[cellpadding]" cellspacing="$stylevar[cellspacing]" border="0" width="100%" align="center">
...
</table>
(including the table tags) and paste it under the last the last closing table tag.
Now, for your first article, you need a title. Replace %ARTICLE1_TITLE% with your choice for the title. Now that you put your article's title down, it's time to do the content. This uses standard HTML, so you need to remember that more than one space will just show as one space and you should use the following tags for things you want to do:
The PHP Code I used for; bold, italics, line breaks, and underlines was:
line break: <br />
bold: <strong></strong>
italics: <em></em>
underline: <span style="text-decoration: underline"></span>
The content that you type up will replace %ARTICLE1_CONTENT%.
Once you're done with your page, save the template. If you want it to display for all styles, you will need to copy the template contents (and title) to a new template within the other styles. The URL for the page will be something like http://Example.com/forum/misc.php?do=page&template=%TITLE% where %TITLE% is whatever came after "custom_" in the template's title. So a template named custom_lolz would have a URL of http://Example.com/forum/misc.php?do=page&template=lolz.
I hope this helps, sorry it's so long >_>