By default, you have one type of category: regular. Suppose you wish to create another group called 'special'.

First, go to Admin Panel -> Settings -> Categories. 'Category Types' is near the top. Add a comma after the 'regular' you see there, and type your new group (do not leave a space). In this case, we'll now have 'regular,special'. Also choose the friendly english display language for it which will be used on the edit/submit category pages. Save your settings.

Next, edit your 'main index' (main.tpl) template. In order to create a unique style for this category type, copy the style which has been used for regular categories and change it to fit what you wish for your new group. For example:

<!-- BEGIN SPECIAL -->
<blink><b>Extra special type of category: <a href="http://scripts.webmastersite.net/wsnlinks/wsnmanual410/{CATURL}">{CATNAME}</a></b></blink> <br />
<!-- END SPECIAL -->

By placing that HTML where you want it, you can make the special categories appear in a special place such as at the very top.

Note that category types only apply to the top level categories, not to subcategories.