Just go to the profile of the person you want to ad, by clicking on the user name. Then go all the way down in the profile to the section where it says

Add XXXXXXXX to my buddylist (click on it)

Once done that it will ask you the following

Add user XXXXXXXX to your buddylist?

Add Cancel

Click on the "ADD" button and a notification will be sent to the user...once that user gets the notification is up to him/her to approve the buddylist request.

Regards!!