Add Featured Image
Adding a feature image to a post is important because it the first visual seen and what other websites pull from your post. You can add a feature image in the sidebar of your post editor.
If you don’t see the sidebar, click on gear icon in the top right-hand corner to access the Document sidebar. Scroll through the sidebar options to access the Featured Image box.
Note: On some themes, you can also enable/disable featured images from showing on your blog posts by toggling the control under Appearance > Customize > Blog Posts > Display featured image