The API allows HTTP GET, HTTP POST, and HTTP DELETE calls.
GET is used to retrieve data (JSON format), POST is used to add/update data (for example, adding a new alert subscriber), and DELETE is used to delete data (for example, deleting a user).
All of the GET API calls can be easily tested with a browser (just paste the full URL and you will receive the JSON output on your screen).
For POST and DELETE, you will have to use cURL, write your own code, or use the tools available for working with REST API calls.
The paths presented here are relative to the root path of Redash.
For example, if my Redash is located at myredash.mydomain.com and I'm interested in the API located at /api/alerts, then the full URL will be http://myewdash.mydomain.com/api/alerts ...