Hi, Please let us know how can we help you.
In case you are not able to see preview of images thumbnails you need to set the featured images in blog posts for that.
Just set featured images, update the post and you should be able to see the thumbnail of the images. Here is a screenshot of the same for your reference.
http://awesomescreen....com/0ee2t4dz6a
I hope that helps. Thanks Aarav