How to use JWT is documented in great detail with our Developer Guide. I will refer you to the following resources to learning how JWT works on a variety of different levels.
1. Here is a page from our getting started section which walks you through the process of [creating an JWT credential][1].
2. Once a credential has been created, the JWT Quick Start guide in our Authentication section covers [how to use it within your code][2].
3. Finally, for a detailed walk-through of JWT, in case you need to implement the protocol in your own home-grown SDK can be found here:
https://developers.ringcentral.com/guide/authentication/jwt-flow
But there is one other thing that should be mentioned given comments below: please make sure JWT is the best auth method for your application. JWT is designed for server-to-server auth. And while you can use it in other use cases, it was not designed for them, and therefore may have unintended consequences -- like creating the challenge of collecting and managing tons of JWT credentials on behalf of users. If you find yourself in this situation, you are encouraged to look more closely at the authorization code flow.
[1]: https://developers.ringcentral.com/guide/getting-started/create-credential
[2]: https://developers.ringcentral.com/guide/authentication/jwt/quick-start