Here’s an interactive tutorial
** Best experienced in Full Screen (click the icon in the top right corner before you begin) **
https://www.iorad.com/player/2289543/How-To-Set-Featured-Image-To-Blog-Post—WordPress–EN-0018-
6 STEPS
1. The first step is to open Dashboard and click All Posts
2. Choose an existing post and click Edit
3. Scroll down and click Set featured image
4. Let’s select an image from your hard drive. Continue by clicking Select Files
5. Select an image from your hard drive, then upload it and click Set featured image
6. Scroll up and click Update