1. First, we must add the REST UI module to our Drupal site so that we can easily configure our endpoints:

cd /path/to/drupal8
composer require drupal/restui

2. Go to Extend from the administrative toolbar and install the following Web services modules: Serialization, RESTful Web Services, and REST UI:

3. Go to Configuration and click on REST under Web Services to configure the available endpoints.

4. Click on the Enable button for the Content row:

5. With the endpoint enabled, it must be configured. Check the GET method checkbox to allow GET requests. Then, check the json checkbox so that data can be returned as JSON. All endpoints require a selected authentication provider. Check the cookie checkbox, and then save it:

6. Any RESTful resource endpoint enabled will use the same create, update, delete, and view permissions that have been already configured for the entity type. In order to allow anonymous access over GET for content, ensure that anonymous users have the View published content permission.
7. Using cURL on the command line, a piece of content can now be retrieved using the RESTful endpoint. You must pass ?_format=json to ensure that the proper format is returned:

curl http://127.0.0.1:8888/node/1?_format=json

{"nid":[{"value":1}],"uuid":[{"value":"9a473f09-fa61-42c9-b4ad-f24b857d04f6"}],"vid":[{"value":51}],"langcode":[{"value":"en"}],"type":[{"target_id":"page","target_type":"node_type","target_uuid":"8a8ad160-69dc-453f-bc11-86775040465e"}],"status":[{"value":true}],"title":[{"value":"Example node"}],"uid":[{"target_id":0,"target_type":"user","target_uuid":"e31b3de2-2195-48c6-9a5e-ab0553461c93","url":"\/user\/0"}],"created":[{"value":1500650071}],"changed":[{"value":1500650374}],"promote":[{"value":true}],"sticky":[{"value":false}],"revision_timestamp":[{"value":1500650374}],"revision_uid":[{"target_id":1,"target_type":"user","target_uuid":"2d7ee3ef-6f8a-4feb-a99a-4af8cfd24402","url":"\/user\/1"}],"revision_log":[],"revision_translation_affected":[{"value":true}],"default_langcode":[{"value":true}],"path":[],"body":[{"value":"Defui dolor elit jus luptatum. Ad augue causa hos loquor luctus minim singularis sino utinam. ","format":"plain_text","summary":""}]}