As full stack web framework Remix provides APIs to deal with common web server use cases. This post will focus on sessions and why and how you can use Upstash to store them.
What is a session?
The Remix docs have a very good introduction to sessions https://remix.run/docs/en/v1/api/remix#sessions
In a few words - sessions are a mechanism that allows the server and the client to share user data / state. Example of session uses are tracking user authentication state, shopping carts status, flash messages etc.