Here’s how:

1. 2 options to open “Add Contact”:
   
   • Click the + in the upper-left corner of the Messenger window, or
   • On your keyboard, Ctrl+Shift+A also works!
2. Enter the Yahoo! ID or Yahoo! Mail address for the contact. Or, for a Windows Live friend, click the first pull-down menu and select the Windows Live icon, then enter the friend’s ID. If you don’t have any of these, but you do have some other email address, use that—they’ll get an email invitation.
3. Then click Add.

Note: The contact is automatically notified and given the option to allow or deny your add request. If the contact denies your request, they won’t appear in your Messenger List.