After signing into Windows Live Messenger, you can begin to add, remove, block, or modify your contacts (Your contacts are the people that you've set up to communicate with using instant messaging.) .
Click the Add a contact or group button , and then click Add a contact.
In the Instant messaging address box, enter the e-mail address of the person that you want to add, and then click Next.
Add a personal message to your invitation if you want, and then click Send invitation.
Click Close.
Notes
If you are adding a Yahoo! Messenger instant message address, enter the full e-mail address.
You may see two entries for the same contact. This can occur when you add a Messenger contact who uses both Windows Live Messenger and Yahoo! Messenger. To determine if a contact is using Yahoo! Messenger, open a conversation window in Messenger. If there is a Yahoo! Messenger icon next to the contact's display picture, they are using Yahoo! Messenger.
When you send a message to a mobile device, Messenger first sends an invitation to the mobile device contact to exchange messages with you. The mobile device contact must accept the invitation before they can receive your message.
In the Block list, select the contact you want to unblock, and then click Allow.
Click OK.
Note
A blocked contact may not be removed from your contact list. In this case, to unblock the contact, right-click the contact, and then click Unblock contact.
Note
If you and a friend want to add one another as contacts and you both have child safety settings (Customizable settings that help parents to protect children from being exposed to inappropriate web content. For example, parents can block or allow websites by web address or category, and limit the contacts allowed in a child's account.) set for you by your parents using Windows Live OneCare Family Safety, you both must ask your parents to add you to one another’s contact list before you can send messages to one another.