You can install Comments via the plugin store, or through Composer.
To install Comments, navigate to the Plugin Store section of your Craft control panel, search for
Comments, and click the Try button.
You can also add the package to your project using Composer.
composer require verbb/comments
You can try Comments in a development environment for as long as you like. Once your site goes live, you are required to purchase a license for the plugin.
For more information, see Craft's Commercial Plugin Licensing.
Available for Craft 3. Get it from the plugin store.