In map maker on the Objects tab there should be a button called "New Gate" that will create a portal. In the Gate Name you type the map the portal will take you to. In where the X,Y,Z is where you will appear on the other map. So go onto the map ur wanting the portal to take you and put an object where u want to appear, copy down the coordinates of the object then go to the previous map, go to the object tab and type the coordinates of the object. So in steps do the name, coordinates then the New Gate. If u find this confusing tell me and ill make it more understandable.