The Address Book application, usually found in the dock, is a completely separate application that allows system wide access to its contents.
Any application requiring names and addresses can access the Address Book, Apple MAIL uses the Address Book in this way.
What you "may" be missing is the function that automatically adds the email address of someone when you start to type their name in the address line. This is a "recent addressees" list that is not connected to the Address Book but is based on emails sent and received.
Of course, for names and addresses to be in the Address Book, they would have to have been added.
By the way, there are three Mac specific forums in this group.
Mac Hardware: Found Here
Mac Software: Found Here
Mac OS: Found Here
Posting your Mac problems in the relevant forum will expose your questions to more Mac users.
Still need the answer to the question in my first post, how was the upgrade done.