Thumbnail Picture in Features???

I have been starting my blog recently and have run into a problem with my theme. I am adding pictures to my posts but when the link to post with some of the content is viewed on the main page the thumbnails are not shown along with the text. It is also not shown in the “Features” section I have at the top. I would like the images to be seen alongside the text on the main page as well. Where in wordpress or in the theme editor would I make this possible?

To see what I mean, view it here:

All that is shown is a small grey box in the top left corner.