How to make a post format in Twenty Sixteen?

I’ve made post formats before on other themes and custom (ground-up) themes, but I don’t understand how this works for Twenty Sixteen, which I’m doing a custom modification of right now. (note: I’m not an expert or trained — I learned WordPress and code myself from YouTube and other tutorials, and trial and error).

I want to have a “link post” for Twenty Sixteen, but I don’t understand where to put it etc. The theme already has all the formats set up, and the options display in the post editor, but when I select link and upload a content-link.php file, it doesn’t change the display of the post.

Any thoughts or suggestions? Or can you point me toward a tutorial?