If you are just about ready to go live and want to start the process of either connecting your domain or migrating a blog but don't want your full site accessible just yet you can create a landing page that visitors will see while you finalize your design.
First, create a new page to serve as your landing page. To do so, click on the "site" tab, you will then see, on the left, a list of pages within your site.
You can click "+" icon to and create a new page.
If you double-click the Page, you will be able to change its name.
To set up a simple landing page I am going to add a background image to both the mobile and desktop designs
(for larger image: Right Click>Open Image in New Tab)
You can add text or other elements to design the landing page to let your visitors know that your new site is launching very soon. Then under the Canvas tab, set the Canvas Type to "Window Height" on both mobile and desktop views to allow the canvas to fill the dimensions on any given screen.
Finally, select the options menu (...) to the right of the page name and choose "Set as Homepage".
As an additional feature, you can create a simple contact form to capture clients' info while the rest of your site is being built.