Using Xara Hosting or Magix Online World:
Click on Publish on the top toolbar, and sign in:
Click on 'Password protect...'
This will take you to the WebFTP control panel for either Xara hosting or for Magix Online World, and into the directory that you've entered into the Optional sub-folder field. If you've left it blank, it will take to into the root folder.
Enter your password for this folder and click on 'Save' to set it. When you then visit the address above, it will prompt you for the password.
Click on 'Delete' to remove the password from the folder.
It's only possible to apply a password to a whole folder, and not to individual pages. This means if you have some pages like a members section, you'll need to split your website between pages that you want password protected and pages you don't, and upload your password protected pages to a new folder.
Using an alternative host
Xara doesn't have any native tools or functions to password protect your pages, as normally this is a server side facility. There are several ways however you can still achieve this.
Using the HTACCESS file
This is essentially how the Xara and MOW hosting above works. You can edit the HTACCESS on your host to set a password on a folder. There are many articles online that can help you with this, for example: http://www.htaccesstools.com/articles/password-protection/
Using a Widget
There are a number of different methods to password protecting your site, please see this website on some widgets you could add to your site: https://mashable.com/2008/05/03/5-free-tools-to-password-protect-your-sites/