Sessions in Flask, how to solve the problem?

Question

Flask

I'm trying to write a website using Flask. The question is how to create variables so that they are used for each user?
Example
I need, for example, a username and password to be added to an array and passed. How to implement this for each user if they are on the site in parallel? It seems that sessions are needed for this, but I can’t figure out how to work with them. I
’ll be glad if you help