To use Backnow you need to have a WordPress 4.0 (or higher version) site with PHP 5.4 or more running on your hosting server. If you’ve already installed WordPress on your server and your site is up, that’s great. For help regarding WordPress installation, please see this WordPress Codex link. To learn about some important stuff you should do after installing WordPress, see this post (on our blog).
Some more resources from WordPress Codex: