“Yes, Mother,” said the child. “It is the great letter A. Thou hast taught me in the hornbook.” please explain

Question

This is a quote from "The Scarlett Letter" by Nathaniel Hawthorne. Hester's daughter Pearl said this to Hester.

Answer 1

A hornbook was a cheap alphabetic teaching book with pages made of thin layers of cow horn.

Answer 2

it has to do with the scarlet letter that hester has to wear...thats all i get out of it....