Drupal 7 greatly simplifies the comment system, especially for site visitors. Comments can be applied to any content type and can be modified for all instances of the content type by selecting the Comment settings tab while editing the content type:
In Drupal 7, there are three basic settings for how comments are handled for a content type. These are modified using the Default comment setting for new content drop-down list:
The Hidden option prevents any existing comments from showing on the site and prevents visitors from adding new comments. The Closed option allows existing comments to be shown, but visitors cannot add new comments. The Open option allows visitors to both see and add comments.
These basic settings can be overridden for each instance of the content type by accessing the comment settings when you add or edit the node.
You can also edit the display settings for comments within the content type. You can determine if messages should be threaded or displayed...