Once you set up a blog page in the Site Builder, you can choose which blog page is displayed when people go to yourdomain.com/blog. You can change this within the blog settings section of the blog control panel.
Click on the Blog icon, then click on settings.
Under the general tab, you will see a section for blog link, and a drop down for what page you would like domain.com/blog to link to. Select from the drop down menu and click save changes.