If you would like to add an additional email account using the Mail app for Windows, then simply:

  1. On Start, tap or click Mail.
  2. Swipe in from the right edge of the screen to open the charms
  3. Tap Settings.
  4. Tap Accounts.
  5. Tap Add an account, choose the type of account you want to add, and then follow the on-screen instructions.

For more information, please visit: http://windows.microsoft.com/en-us/windows-8/add-accounts