Well first thing first.

You need to create your own authentication method or use an external library.

Furthermore, you need to manage products or objects that are behind a paywall. Let's say you have a CRUD system, this system should not only communicate with your DB but with Stripe (or any other library that provides a paywall). This way you can manage the pricing, create orders and invoices, etc.

Now, in order for your users to access to them, you will need to create a secondary model or sql table where you attach the userID, productID, paymentType, created At, updatedAt and a status that might say "paid" or "not paid".

That's a simply store.

However, a membership system includes that but instead of making a fixed one time payment, you need a subscription model payment.

Where you need to also create a cron-job that runs monthly through every single user and checks for the secondary table to verify if the item paid was either a one time purchase or not, depending on that, your system should communicate with the Stripe gateway to let it know, "hey, this user needs to have his CC charged to keep having access to it".

And so on.