You have a number of tools available to manage interchanged layouts. On the Interchange form, the first tab (Other Layouts Linked) will show you al list of all interchanged layouts in the system. This list will allow you to see all the towns on the other's layouts, and all the industries within those towns. Clicking on each industry will show a list of all shipments from your layout to that industry.
Within each layout list, below the towns, you will see two other choices. "Pending inbound shipments for here" and "Outbound waiting shipments from here". The first item will show you what shipments from that layout are about to be executed. They have been imported, but not yet executed. You have the option to delete any one of these shipments before they happen.
The second item is shipments that are ready to head off your layout. This list of shipments is when the loaded car arrives at the portal to the other layout. They will stay there loaded until you export to the destination layout.
On this tab you will also see the details of the selected layout and selected. If you have had enough of this other layout, you can delete it. Deleting a layout will delete all shipments set up to go there.
You will also see a button "Match Car Types". Because there are two lists of car types to use in the program when you first started, if two interchanging layouts use different car types, there is going to be a mismatch between the two layouts. That is, if my layout uses the simple car types, shipping a BX of goods to another layout, and that layout uses the detailed car types, where the equivalent could be any one of a number of boxcar types, such as XM. This will also occur if you create you own car types that do not exist on the other layout. You need to match up the car types between your layout and the interchanged layout so the shipment can be "transferred" to the correct car. This will only be a problem if you interchange virtually, as no car is physically moved to the other layout. There is a section on creating shipments between yours and their layout which shows how to deal with this problem.
Simply check a car type (or more) from your list (left), and a car type (or more) from their list (middle). Pressing Match Up will send the matched pairs of car types to the right list. Checking any of them and pressing "Remove Match" will do just that.
Also on the Interchange form is a tab showing which foreign cars are ready to ship home. These will be other layout's cars that are on your layout that have finished their shipments and are currently sitting at a portal. This will allow you to package up those cars to send home.
To change or set the portals from which cars come and go on your layout, press the button on the top right of the form. A portal is any place on your layout were cars come and go to other layouts. This could be an interchange location on your layout which you model as a junction, or could be any yard that facilitates shipments.
This form will appear showing the linked layouts you have on the left and the places cars come and go on the right. Simply select the layout and check the portals. When you create a shipment to this layout you will get the checked portals as a list from which you select one to send the shipment through.
The last tab on the Interchange form is a log of all the interchanges you have done.
One other item you will need is the ability to know who's other layouts your cars have gone to. In the Admin form, on the Equipment Location tab, the left list at the bottom will show you what other layouts cars that have left have gone. If those layouts have subsequently sent your cars to another layout, this obviously will not know that.