Exposing Virtual dataset as an API

Can you please let me know how can we expose virtual/Physical dataset as an API

The Catalog REST API (http://docs.dremio.com/rest-api/catalog/) allows creating/updating/deleting of datasets. The SQL API (http://docs.dremio.com/rest-api/sql/post-sql.html) allows you to run queries against datasets.

How can generate authorization key on dremio in order to access data as rest api? I need pass detail on postman for same.

Our REST API docs (http://docs.dremio.com/rest-api/) have all the information you need. Authentication is covered here.