It's easy to add a contact to your Messenger List, here's how:

1. Click Add at the bottom of the Messenger List, then click either Yahoo! Contact or Windows Live Contact. (You can add either type.)
2. Type or paste the person's Yahoo! ID or Windows Live ID in the box that opens at the top of your Messenger List.
3. Press Enter.

The contact will get an invitation and can either accept or deny your request. If they deny your request, you won't see them in your Messenger List. (Your Messenger List can hold up to 300 contacts.) When you add a contact to your Messenger List, the contact also gets added to your Yahoo! Address Book.