Facebook Like Box and some other plugins require admin id for meta information.
Suppose for like button plugin required admins id in the meta information:
So if you create your page by your facebook account then at first login to facebook. Find account tab from the top right navigation bar. Click on down arrow symbol besides account and then click on account settings. Then you will find
Username : http://www.facebook.com/your_id_name
So your_id_name is your admin id or user id.