Stripe is both incredibly simple and very complex to implement. I'll write a full blog post on this at some point soon but, in a nutshell
Stripe Checkout makes it incredibly easy to add subscription billing. Simply set up the products in Stripe and copy/paste a few lines of code in to your application
Subscribing is only part of the story, you also need to enable users to upgrade, downgrade and cancel their subscription. Stripe provides an API but you need to implement the required functionality in your app.
Your app also needs to handle failed subscription attempts, failed payments, and many other scenarios, otherwise you run the risk of not being paid by users of your app, or of charging users when they are no longer users.