To enable commenting on your WordPress website, you should go here: http://www.mydomain.com/wp-admin/options-discussion.php to change the discussion options (to turn commenting abilities on or off) on your WordPress website.
Also, you can check the checkbox beside “E-mail me whenever” that says “Anyone posts a comment”. You will get a notification if someone writes a comment on your blog post.
Then, go to an old post you’ve already published, and click the “edit” link. In the top/right of the WordPress dashboard screen you will see “Screen Options”.
Make sure the “Discussion” checkbox is checked.
Then, at the bottom of the post edit page, there will be a checkbox that says “Allow comments.” You should check that if you want that post to allow comments to be made on it.