By default, comments are turned on for both static pages and blog posts. This tutorial explains how you can turn off comments for single posts and pages as well as turning comments off completely.
Deactivate comments for a single page or post
You can simply turn off comments for a single page or post in your WordPress backend. Therefore please go to Pages → All Pages and hover over the page which should have no comments. There will appear some links undearneath the page title where you can click on Quick Edit.
You can then see a Allow Comments checkbox on the right where you can deactivate comments. This method works also for blog posts.
Remove comments for several pages or posts
If you want to turn off the comments on all your pages or posts you can tick every page/post and then select Edit in the Bulk Actions select field above the pages table. Click on Apply and select Do not allow on the Comments field. You can save the change on all your pages at once by clicking on Update.
Deactivate comments for new posts
Please be aware that WordPress will activate comments automatically for new created posts. You can turn off that feature on the discussion settings, which you can find on Settings → Discussion in your WordPress backend.