Push Notifications API Functions

Can anyone help clarify what each of the API functions do? The documentation is extremely sparse on … well any sort of description of what each function is responsible for and why/where they should be used.

This is the documentation I’m referring to: https://capacitor.ionicframework.com/docs/apis/push-notifications/#api

I understand the listeners and register functions, but what are the channel functions for? And why/when would you use the deliveredNotifications functions?

Thanks in advance