Instructions
Sign in to Xbox Live with your Gold Family Pack primary account. Toggle to "Settings" and then select the "Family" icon. Select the "Add a Family Member" option. Select "Available: Add Gold Family Member" under Your Gold Family Pack.
Scroll through the list of gamer tags to select the person if he already has a gamer tag on the Xbox. Select "Create New Profile" if the person doesn't already have a gamer tag on this Xbox. If the person is new to Xbox you can create the account by following the onscreen instructions. If the person already has an Xbox Live account you will need the Microsoft account and password.
Read the final screen to see how much time is added to the Gold Family Pack if the new member already had an Xbox Live Gold Membership. The Family Pack membership is extended by one month for every two months remaining on the new member's old membership. For example, if the new member had four months remaining, then two months is added to the Family Pack membership period.