ENABLING COMMENT MODERATION

Comment moderation is enabled in Settings - Site information, by setting the  "Moderate Comments" flag in "Navigation options".

Comments for a single content are enabled in the related Content Form, by setting "Activate Comments" to Yes in the "Other Information" tab:

If you wish all contents for a category to have comments automatically enabled, set the "Activate comments" flag in "Default content settings" in the Category Form. This setting will only change behavior in contents you add further on.

MODERATING COMMENTS

When you access the Moderate Comments form, all user comments are displayed by descending date.
Click on the edit icon, approve the comment and save.