I will be interested to see the replies you get to this myself. In the meantime this may be of some help:
Microsoft's Address Book / Contacts is the People app. You should have that available as a tile in your Start screen and / or All Apps. In Mail I have not found direct access to People but I have found you can do some things by opening the online email utility which is Outlook.com. It should have the same emails in it as Mail. Again I have not found People directly there, but on the upper left is a group of coloured squares. This is a short-cut to all the online Microsoft Office features, including People. If your apps have been synchronizing your contacts should be there.
Another thing you might try is to see if you have got Windows Live Mail (.eg. as a Start screen tile). If you have, in the bottom left corner there should be icons, one of which is a Book --- it is your contacts, same as People. Live Mail is good, but I think it is in process of being scrapped.
Also, have you registered your Yahoo Account in Mail? Click on the Settings cog bottom left. Setting open on the right. Go to Manage Accounts and then Add Account. I have added a BTYahoo Account and can use both Mail and BTYahoo emails (or others if I want) together in Mail.
As I said, I will be interested in anything others contribute, including any corrections to what I have written.