To use the Lagoon for Divi WordPress theme you need to have a WordPress 4.0 (or higher version) site with PHP 5.6 (preferably PHP 7 or higher) and MySQL 5.0+ 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 read through the WordPressWordPress Codex.
In addition, you must have the Divi Theme 3.0 (or higher version) by ElegantThemes installed, preferably with the Divi Builder as well.
Some more resources from WordPress Codex: