Here there is a good video tutorial by MediaCurrent about Restful API in Drupal 8 Core

http://www.youtube.com/watch?v=TLHP9doaZ98

In the tutorial, Peter Mallett used Dev HTTP Client Chrome App for making HTTP requests.

When requesting for entities (content), GET was used

GET <YOUR-DOMAIN.COM>/entity/node/1

with this HEADER:

Accept:application/json

When requesting for entity (content) creation, POST was used

POST <YOUR-DOMAIN.COM>/entity/node

with this two HEADERS:

Content-Type:application/hal+json X-CSRF-Token:<YOUR-TOKEN>

Token can be obtained, when logged, by visiting

http://<YOUR-DOMAIN.COM>/rest/session/token

Here is a HAL+json code needed to create a content of a basic content type:

{ "title":[ { "value":"Test" } ], "_links": { "type": { "href": "http://<YOUR-DOMAIN.COM>/rest/type/node/your-content-type" } } }

Source: Drupal 8 Restful Services