It locks your files and demands payment for the key. Paying frequently returns nothing, which is why a backup kept somewhere separate is the only defense that reliably works.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a padlock fitted to your own front door.
For example
Every photograph on the computer is locked and a message asks for money. The people who paid mostly got nothing back.
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.