[theme: twenty eleven] how to make posts be summaries on blog page

I am in the process of setting up the blog portion of a small website
http://riverlogicpartners.com/river-logic-blogs/

The blog page currently contains three FULL blog posts which is NOT desirable. These posts need to be summaries with a ‘read more’ or ‘continue reading’ link underneath each post excerpt.

In the Dashboard, I noticed under “Reading” something that says “For each article in feed, show full text or summary but realize that this isn’t the same thing.

How exactly can I make the Blog page only show blog post summaries with links to each full blog post (using the twenty eleven WP theme)?

Thank you so much!