Create excerpts and thumbnails

Hello all,

I am a beginner of WordPress… learning to make my site.
I have a page showing all my published work, anyone know how to show my posts with excerpts and thumbnails like this website:
http://www.thenewsoutlet.org/category/community/

I have tried posting on the excerpt and featured image, but nothing show up…prob have to do with my theme?
I also tried using a plugin called Excerpt but it doesn’t work either..

this is the page of my site:
http://www.sheewaiwong.com/clips/

Hope you can guide me through this..
Thank you!