Double-clicking on a controller in the configuration diagram opens the Controller dialog. Alternatively, choose Controller... from the Edit menu, and select the desired controller from the list which appears. Select the Create... button in the Strings/Devices section to display the Create String dialog. Fill in the information and press OK. Strings and their I/O devices created from the Controller dialog are not automatically connected and defined to the selected controller. Instead, the String dialog appears, where you can choose how to connect the string's interfaces.
If there is more than one physical description possible for the string, pressing OK will first display the Choose Physical Description dialog before the connection dialog.