You may want to enable comments on your site to encourage a discussion, but you may just be presenting information and not want any comments. No matter what you want to do this doc will get you going with comments.
Turning Comments On and Off for the Whole Site
You can turn off comments for all pages and posts you create in the future. Note, this will not effect pages and posts you have already created. See below for how to turn those on and off.
1. Log into your Dashboard and go to “Settings – Discussion”

2. From there you will need to un-check the “Allow people to post comments on new articles.”

3. Scroll down to the bottom and click “Save Changes.” You can find out more about all the other discussion settings on this page as well.
Tun off Comments on Pages or Posts you Already Created
The default when you create a new site is to allow comments on all new pages and posts. If you have already created the page and want to turn comments off:
1. Log into your Dashboard and go to the listing of Posts or Pages by clicking “Posts” or “Pages”
2. Hover over the title of the item you would like to turn comments off on. You will see a “Quick Edit” link appear below the title. Click that.

3. Un-check the “Allow Comments” box on the right hand side.

4. Click the “Update” button to save your changes.
You will need to repeat this action for each page you want to turn comments off on. You can also read more about the “Quick Edit” features here.

2 Comments
Is there a reason that the ‘Allow Comments’ flag is not available in the ‘Detailed Edit’ screen? Seems a bit silly for it not to be on the main edit screen if you rarely use the quick edit option.
I stand corrected, you just need to have the Discussion setting enabled in the Screen Options for the page editor to see the comments flag.