You'll need the home page you created earlier when doing this step. Don't worry that the home page you made is just a placeholder. You will eventually fully design it in Bricks. Right now, for the Seed site, all you need is the placeholder home page you currently have.
By setting excerpts in feeds you make it slightly less convenient for people to steal your content (although they still can do so by other methods).
You should set the search engine visibility to off to try to prevent your seed site from being indexed, or if you are building a real site, to prevent it from being indexed before you are ready.
Go to Dashboard → Settings → Reading
Make changes to WordPress Reading Settings.