You will use the Article content type provided by the standard installation. Following the preceding recipe, Enabling RESTful interfaces, you should have the REST UI module added to your Drupal installation using Composer. This can be done with the following command:
cd /path/to/drupal8
composer require drupal/restui
In this recipe, the Drupal 8 installation is accessible through http://127.0.0.1:8888. Use the appropriate URL for your Drupal 8 site.