If you want to protect your WordPress blog with AuthPro and create accessible by members only pages or posts you can install AuthPro plugin to your WordPress website.
You can download latest copy of AuthPro WordPress plugin at WordPress plugins directory or install it using 'Plugins' menu in WordPress admin panel (search for 'authpro' keyword).
With this plugin you can easily protect your entire website/blog or individual pages or posts. You can also disable protection at any time if you need.
Please note, you can't protect hosted wordpress blog on wordpress.com website due to JavaScipt security limitation of this blog service. Instead, you need to use WordPress script installed on your own website. You can download it's latest version at wordpress.org website.