Featured posts are missing

Hello! I am quite new to wordpress and can’t figure out one thing.
I use Kale theme (which I think is great!), and would like to show featured posts on my frond page. I go to Appearence -> Customize -> Front Page -> Featured Posts and choose to display my featured posts. But the drop-down list under Post1, Post2, Post3 is empty. What should I do to populate this drop-down list with my posts? How can my make my posts featured?