Hi,
open up the mail app and then click on the 'Charm', settings (obtained by placing cursor top or bottom right then click on the cog wheel). Near the top you'll see Accounts listed, click that and then add your account.
Going back to the sign in with a microsoft account. It does give a different side to win 8 if you get your self a hotmail/outlook account (otherwise known as a Microsoft account) You'll be able to use the sign in for windows 8 so your always synced with your files plus the account will grant you further access to other microsoft goodies like messenger etc.