Locking / Hiding / Password Protecting Your Store
From Spiffy Stores Knowledge Base
Password protecting (or hiding) your store will lock it, and hide everything so you can continue setting it up. Some themes will also display a "Coming Soon" splash page.
Password protecting your store is a good idea while you are still adding products or designing its look and feel. This is especially important if you have set up a credit card and payment gateway but don't want to start accepting sales quite yet.
Your store can be password protected in the Preferences -> General Settings -> Password Protect Access to your Store section of your store admin.
Set the password, enter a message to display to visitors, and click the "Save Settings" button. Your theme may also have a section for styling your password page. Most allow you to set a background image.
When your store is ready to go, you can then simply un-tick the Use password protection option and click the Apply Settings button.