Enabling password protection requires all visitors to enter a password before gaining access to the contents of your store. The password is shared and set from the administration settings.
Go to Settings>General Settings>Password Protection
To password protect your store, click on "Visitors require a password to enter" and enter your password you want to use. You can also add a message that your visitors will see before logging in. Once completed, click on the Save Settings button.
Now that password protection is enabled, all new visitors that have not logged in will be prompted to enter the password you set in the first step before viewing your site.