How do I understand storage on my devices and in iCloud?

A Member recently asked me the following stream of questions.

I thought it would be useful to post the chain here and on the NaplesMUG Yahoo discussion group.
Feel free to add your own commentary and/or questions, of course.
Do you think it might be useful to have a short course on apple data storage?
for example, here are a few questions that might be addressed:
     what apps use apple data storage, and which don’t?
      and how long does the apps’ meter run, once it is opened?
                      which apple apps on my iPhone are using data storage, or would use it if i opened them?
     does swiping up from the bottom (on an iPhone) turn off data storage for an app that is using it?
      if i open an iBook, does that app continue to use data storage while i have it open and am reading it?
      how much data storage is used by an app that is running “all the time” (i.e. 1password)
      are there any good tips to manage apple data storage better?
GREAT IDEA… I will add for the October meeting
I assume you mean by “Apple data storage” iCloud storage?
If you are asking about RAM that is a very short answer.
I guess I am confused.  
I purchased the 50GB option for iCloud storage. Of that, I am using about 6 GB.
Nevertheless I get text messages from Apple near the end of every month that I am nearly out of data storage.
Am I not understanding what they are telling me.
welcome to the world of Apple!

On your device, there is a really easy way to check what they are talking about.
Open SETTINGS (of course – it is our GO TO place)
See how much is used ON YOUR DEVICE
After a while, it calculates which apps are using storage on your device. It will even make some suggestions about offloading some unused apps, and their data. Usually this is where the storage issue and the error message originate.
The bar graph shows you your use of the iCLOUD STORAGE your purchased.
Beneath that graph is MANAGE STORAGE
Click it
It will take you to the apps using iCloud storage and how much they use.
If you click one of the gray arrows, it will show you the contents of the app’s storage.
More importantly, if you click the BACKUPS storage arrow, it will show you how much you backups are using.
Note that you might even be using storage to store a backup from an old device!
Let me know if this helps.