How to properly store a JWT token?

Question

JSON Web Token

I decided to use a JWT token in the Slim Framework web application, but I never used it before. Can you briefly explain how and where to store a JWT token?
Let's say there is a backend that implements a certain API. After authorization, the backend issues a JWT token to the web client. When the web client accesses the backend, the JWT token must be present in the request header. If the token is missing or invalid, then the request is ignored. This is a general scheme for working with a token.
How to store JWT token? Like a regular token? Why does slim-jwt-auth have a persistent private key in the options?
Thanks in advance for your replies!