Your files sit on a company's computers, so the same copy opens on any device. That also means deleting on one device deletes everywhere — it is storage, not a backup.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a locker at the station instead of a shelf at home.
For example
You take a photo on your phone. You open the laptop and the photo is already there. You did not send it anywhere — both were looking at the same shelf.
This is one card out of 275.
The hundred words you meet most are free — the whole set, animated, in one file that works with no internet.
Volume 1 has all 275 in fifteen chapters, with Staying Safe the largest chapter on purpose.