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

First, go to your admin panel and click 'manage settings'. Scroll down to 'Comment Types' near the bottom. 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,reviews'. Save your settings.

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

<!-- BEGIN REVIEWS -->
<blink><b>This is a review</b></blink> <br>
{COMMENTPOSTERNAME} says this about {COMMENTLINKNAME}: {COMMENTTEXT}
<!-- END REVIEWS -->

By placing that HTML where you want it and setting 'mix comment types' to 'no' in your settings, you can make the unique types of comments appear in different places on the page.

Now, suppose you decide you'd like to make reviews show in the options on the edit page as "Reviews". You don't have to edit the setting and force yourself to redo your template -- instead, you can customize the display of each setting by filling in the 'commenttypes' language item. On your 'mangage languages' page find that item and fill in the display names in the same order you have the official names in on the settings page.