It wipes the device back to the day it was bought, taking everything not already backed up with it. It is also the only proper way to pass a phone on to someone else.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
repainting a room back to bare white.
For example
You give your old phone to your nephew. First you wipe it, so it starts up asking his name, not showing your photographs.
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.