Your phone lends its mobile connection to a laptop beside it. Careful: a laptop treats it like home Wi-Fi and will happily pull a huge update over your allowance.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
holding your umbrella over the person beside you.
For example
You are in a café and the laptop has no internet. You switch something on in your phone and the laptop works — it is borrowing the phone's connection.
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.