Featured Image
Be sure to set a Feature Image for your post. The Feature Image is what shows up as the thumbnail image on the Posts (CoBlocks) feed on your Post Listing page.
While editing a post, you will have a right-hand rail with editing options. While on a block inside the page, it defaults to the Block settings. You can switch to the Post settings tab if you need to adjust the settings for the Post page.
Click on the Post tab in the right-hand rail to get the Post settings. There are several sections, the Summary which includes the url, publishing status, and author.
After Categories and Tags sections, you’ll see the section Featured Image section. Click anywhere in the “Set featured image” box and the Media Library will pop up. Upload or choice your image and then update your post.
Excerpt
This is the text that displays under the thumbnail image on the Post Listing page. You can copy of paste some of the text from the content of the post or you can craft a unique description.
The Excerpt field is found directly under the Featured Image section on the right-hand rail of the Post settings. See photo to the right.
Be sure to update the post after you make changes.