You will need to authenticate with a user account possessing the 'api user' role. Use Basic Auth.
Run a POST to /api/1/metastore/schemas/dataset/items
with a json formatted request body, the minimal elements are:
{ "title": "My new dataset", "description": "Description for my new dataset.", "identifier": "11111111-1111-4111-1111-111111111111", "accessLevel": "public", "modified": "2020-02-02", "keyword": [ "test" ] }