make a brush out of nodraw (this will be the area that they will have to enter to teleport) and tie it to entity "func_teleport"
from there add a normal entity (point_teleportdestination)
Place that were you want them to teleport to and face the entity whichever way they should be facing...
Open up the setting for the brush and set the destination to the "point_teleportdestination" that you made