The dungeon portal screen allows you to place a one way portal between two rooms of your dungeon. A room may only have one dungeon portal in it but you are free to place as many portals as you wish throughout your dungeon.
To make a portal you must select a source and destination room this is done simply by clicking on the rooms on the dungeon map on the left. You will notice when you click the display updates to indicate a new source or destination you can change these by clicking the Clear button and re-selecting a room.
When you have the source and destination rooms selected click the Place portal button and a portal will then be placed inside the source room which can be used by anyone to get to the destination room.
You can use the delete portal button to delete any portals in the current room incase you decide to remove a portal.
You may only have one portal placed in any one room at any time so plan your dungeon accordingly. Also these portals do not show up on the dungeon items screen this means the only way to delete them is via the portal screen.