There are two ways to register External Resources. Select the New option in the File menu, then External Resource and then you can either
Choose External Resource and define it in the same way as you would define any other object
Choose Bulk Loader option which will bring up the following dialog:
Use the Add button to select one or more files from your disk, or use Windows Explorer to drag and drop files into the Register External Resources dialog.
Provide a prefix to name them all and press the Create button. Note that LANSA detects what folders the files are in.