Interfaces can be started by selecting the realm node where the interface you want to start is running, and select the 'Interfaces' tab. From the table of configured interfaces, select the interface you want to start and double-click on the row. Alternatively, you can click on the 'Status' column for the interface. Both will have the same effect, and will present you with a dialog for starting the selected interface. This dialog is shown in the image below.
Clicking on the 'Start' button, will start the interface on the realm server.