1. Login
2. Click 'admin panel'
   
3. Select page where you want the comments  capability from the 'chose the page to edit' pull-down list.
   
4. Find  what's this? -> Add Words and Images Download Contact Form PHP Code Visitor Comments to Page Now
5. Use the pull down to select 'visitor comments'
6. Click 'to Page Now'

NOTE:

Sometimes you want to use the comments for private review of something.  In that case make the page "private" so that only people logged in with priveleges can see the page and comments.   See help for "webpage manager" to see how this works.