Two different things sold with similar words. Out of storage means delete files; out of memory means close apps. Buying more of one will never fix the other.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
the pantry versus the countertop.
For example
The phone says it is out of space, so you close some apps. It still says it. Closing apps clears the desk; you needed to empty the closet.
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.