The Preview page lets you test how your design and content will look when the site is live, without requiring you to start a paid subscription.
On the Preview page, click the Desktop, Tablet and Smartphone icons to see what your content will react to differently sized screens. Read more about mobile responsive design here.
This is my site previewed on a desktop/laptop device:
This is the site previewed using a Tablet display:
And this is what the site will look like on a smartphone:
When you're happy with the content and layout, go to the Publish page to choose a subscription plan. Continue on the Free plan if you'd like to share a link to your website with friends and co-works.