Short Answer:
During the post creation process you can add a thumbnail to a post, as well as after the post is live.
Steps:
1. Click Create Post and create a post as normal.
2. Click Add Thumbnail to the right of the Title box.
3. Upload a thumbnail from your device.
4. After a post is live:
1. Click the ellipsis (three dots) to the right of a Post’s title.
2. Click Edit Content.
3. Add a Thumbnail from your device and click Next, then Save Changes.
