Hi Anlong,

I hope you are well today and thank you for your question.

You have to set featured image to the post as described on this page http://freewptp.com/how-to-set-featured-image-or-post-thumbnail-in-wordpress/

Also you have to add post excerpt in the excerpt field of post as described in this page http://www.wpbeginner.com/glossary/excerpt/

Best regards,
Shufflehound team