How to add the "comment form" module
Drop the "Comment form" module on your page. In order to have the form working / available, please assure yourself the comments are not disabled in your installation. Check the following:
- On WP Admin > Settings > Discussion the option "Allow people to post comments on new articles" should be enabled.
On individual posts, the discussion option should be also enabled
In the case you don't have such options on your editor page, check the following screenshot to see how to enable them:
Please note that all the posts published with this option disabled, remain with the comments disabled even the settings is changed. Check the next point to see how you can enable again the comments for these posts.