Once you singned into developer portal here https://developer.ringcentral.com/
You will be given a sandbox environment as default to create different applications and test APIs there. You can go through the link given above to start with.
Once the application you created pass all the criteria and rules in the sandbox, you can push that to production later
Using the RingCentral Phone for Desktop, you can dial or receive test calls, send and receive test SMS or Fax messages in your sandbox environment.
Download RingCentral Phone for Desktop:
Tip: switch to the "sandbox mode" before logging in the app:
4 People are following this question.