Installing the Add-on is very easy. In the Atlassian Marketplace listing, click Buy it now (or Try it free if you want a 30-day trial version). Once the purchase process is completed, the plugin will install automatically. After it was successfully installed it will be displayed under Manage Plugins > User-installed Plugins. The add-on will be installed globally across your Confluence system.
If you want to try it out before purchasing, you can obtain an evaluation license key through the Atlassian Marketplace. If you need more time to evaluate the add-on, you can extend your trial period.