How can I go about setting up push notifications using firebase cloud messaging and cloud functions?

Question

I'm been coding for a year now and know swift really well and the basics to javascript. I've built a social media like app and its completely done besides the push notification functionality... which i've been struggling with for quite a while now.

I'm having trouble figuring out how to implement these in order to send notifications like when a user follows another user or they receive a new messege.

I don't understand how to integrate the cloud functions that I would write using and node.js with my xcode project.

When I look for documentation online its usually just how to send push notifications using the firebase notifications console which is cool but doesn't trigger based off specific user actions or events (ex: when the user gets a new follower)

I think since im struggling with grasping the concept of how to implement it, the actual technical set up of it makes even less sense. Any advice or resources would be greatly appreciated.

Thank you