To hide your store from public view while it is under construction, go the the Settings page within your store's Admin section, and select Private from the dropdown menu in the Store section. You will be prompted to create a password for the store. A visitor must know this password to view the storefront. This option can also be used to share your storefront only with certain customers or colleagues. Click Save at the bottom of the page.
To make your store public again, select Public and click Save.