Really easy. Just click on the preview button, depicted by an eye icon, on the shelf.
When you are making changes, edits, or adding content, saving occurs constantly. If you want to take a look at how your site is going, enter preview mode.
Preview mode will temporarily disable all the editing capabilities of your site, allowing you to experience and navigate it as a non-administrator user.
If you want to go back to editing/authoring mode, click on the bottom, where it says “Back to Editor”.
You can also log out (More > Logout) and see your site as any other visitor.