Vanishing excerpt field

I’d like to display only excerpts of posts, rather than the entire article. In Dashboard, I’ve selected to “display summary”, yet I’m still getting the entire article.

On the page where one types up and edits posts, I do see the “manual excerpt” field. I’d prefer not to have to create the excerpt each time. I’d be happy with the default 55 word excerpt.

Is there something we’ve overlooked in order to get the 55 word excerpt working? Will it automatically add a “read more” link to take readers to the full article/post?

Thank you!