The easiest way to obtain credentials is from an existing connector. If you haven't installed one yet, we recommend to install the Incoming Webhooks Connector.
On the installed connector of your choice, select Settings and scroll to the bottom until you find the section which contains the credentials as displayed below:
The Connector ID (1) and Connector Secret (2) are used in the authentication headers of an API call while the Organization namespace (3) is used as part of the URL.