By default, WordPress enables users to comment on pages and posts. You can change this for individual pages and posts.
To change the default,
- go to your Admin > Settings > Discussion
- check/uncheck "Allow people to post comments on new articles"
- Save Changes
To change for individual pages or posts,
- go to your Admin > Pages or Posts
- rollover the page title, click "quick edit"
- check/uncheck "Allow comments"
If you're editing the page or post itself, scroll down to "Discussion" and check/uncheck "Allow comments". If "Discussion" is not visible, scroll to the top right of the screen and click "Screen Options" and check "Discussion".