How it interconnected? (FirePress, Ghost, Mailgun, Membership, Stripe, Payments)

In March 2021, Ghost v4.0 was finally released. It's an eight years old platform build on top of Node JS. You got so much out of it:

the best CMS/blog
a membership 0% fees based on @stripe (recurring revenues). In other words, FirePress doesn't take a commission on top of it. Only Stripe fees apply
a great newsletter platform to send emails to your members
a blazing-fast website
a great theme selection

How does it Work Together?

Ghost is the core software to manage your website.
We at FirePress manages your Ghost installation for you. It's a fully managed service. We are your hosting company.
Mailgun to send transactional emails (newsletter) from Ghost via an API. Those emails are sent to your members. It's managed by FirePress. To see what's included in your plan: Are there any limits on transactional emails?
The memberships are managed within Ghost. You can configure three subscription plans within Ghost: Free, Monthly, Yearly payments. The limitation is that you can have only one plan for a monthly subscription AND only one plan for a yearly subscription. In other words. you can't have a "basic", "regular", "premium" plans. This is not made to sell products but subscriptions.
Stripe is the payment gateway between your clients and your subscription plans. You will need a Stripe account. Then, you must link your Stripe account with Ghost. There is nothing technical here, it's a simple configuration :)