Asumming you are talking about the doors that sort of interlock themselves and getting them to teleport you, then here it is: http://www.forgehub.com/forum/halo-forge-discussion/8108-how-make-door.html?highlight=door Hope this helped. For help in teh future, refer to the forge tutorial master index. It basically has everything you need to know about forging.
Nobody told me either. One less you tell somebody there is a teleporter behind the door it seems ratter pointless because they won't bother walking up to the door. There should be a tutorial like this in forging 101. I have been all around forgehub and havn't seen one thread that explained how. Although I never really cared or went searching for it.