Need to understand how to implement my idea into the app

So I am developing an app as part of a group project. The app has to fetch some data (most importantly time for an alarm) from Cloud Firestore and then ring the alarm at whatever time the alarm is scheduled. This all should happen even if the app is not open right now. I know that I have to use:
1. AlarmManager or WorkManager (still I am not sure which one) for background work like changing the time for alarms and firing the alarm intents
2. Something called PendingIntent (maybe) to set the Alarm intents
3. ACTION_SET_ALARM for actually firing the alarm.

Now what I don't know is how do I combine all these in a manner so that I can implement my idea for the app. I cannot find a single example anywhere where all these things are used together. I would be very grateful if someone could help me.