• Alice gives Bob a Secret Note.
• Alice and Bob agree on a way for Bob to scramble the Secret Note so that Alice can unscramble it.
• Bob scrambles the Secret Note.
• Bob gives Carol the Scrambled Secret Note.
• Carol gives Alice the Scrambled Secret Note.
• Alice descrambles the Scrambled Secret Note.
• Alice tells Carol the Secret Note came from Bob.

Now, Carol trusts Alice and Alice trusts Bob. By passing this note around, Carol can trust Bob since Alice trusts Bob and she trusts Alice.

Passing the note around tells Carol (Web Server) that Bob (Web Browser) has trust from Alice (Attestation Server) and is not some imposter just claiming to be Bob.