If you want to display the featured image of a blog post, like this:

Please follow this instruction:
- Go to the blog post in Admin for editing it
- Scroll down finding a link named "Add excerpt" and click it, like this:

- Click "Insert Image" and choose your image, like this:

- In case you want to put a VIDEO, first please get the embedded code of the video (YouTube or Vimeo), then click <> icon to switch to HTML mode and PASTE the code, like this:

- Save the changes.

Hope this helps!
RoarTheme Support Team.