It means the connection is encrypted, nothing more. Scam sites have padlocks too. Read the address beside it — that is the part that says who you actually reached.
The drawing that proves the sentence above. It is the same card that is in the book.
Think of it as
a good lock on the door tells you nothing about the shopkeeper.
For example
The scam shop has a padlock too. It means the road is safe. It says nothing about the shop at the end of it.
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.