Hi, Karen. Hope all is well. If you go to Settings → Discussion from the admin dashboard, you want to make sure that Allow people to post comments on new articles is checked if you want the comment box to show up on any new pages that you create. If you don’t want the comment box to show up by default, then leave the box uncheccked, and you can selectively choose which pages to allow comments (see below).
If you have existing pages or posts where the comment box is not showing up, go into the page or post editor and scroll down until you see a section labeled Discussion. If you don’t see such a section, then click the Screen Options tab in the upper right corner and check the box labeled Discussion and it should appear. Then check the box in that section that’s labeled Allow comments and the comment box should appear for that page/post.