Chylin it has been long you started XTGEM and you're still battling on how to use images as thumbnails for your blog

Before you post your article all you have to do is upload the image e.g if the article is about wizkid all you have to do is create a folder named "blog_image"
Upload the image you want to use as the thumbnail
Copy the link e.g

http://redbullet.xtgem.com/blog_image/wizkid-star.jpg

Go to your blog click on add post and put the link you copied in the large textarea in this format

<img src="http://redbullet.xtgem.com/blog_image/wizkid-star.jpg"/>

After that paste the story/text under the the above code

On Sunday, November 6, 2016, Wizkid did it again and had the whole country talking about him. In one night, the star received three awards - he won Best African Act and Worldwide Act at the 2016 MTV Europe Music Awards » . That same night at the 2016 All Africa Music Awards (AFRIMA) which held at the Eko Convention Centre, Eko Hotels & Suites, he won Best Artiste of the Year.

see example at screenshot below