How to Create an Inset:
Choose Tools > Monitor.
Select the region that will be depicted. Initially you will see a new window, not an inset. The title of the window reports the central frequency of the selection, which can be changed. The monitor tool is still active, but not necessary. If you are satisfied with the current selection, you can choose Tools > Pointer.
Resize the monitor window and place it over the main window at the same location where you want the inset to stay. The monitor window should not cover the borders of the main window.
Choose View > Fix Inset. This transforms the monitor window into an inset.
The inset of a 2-D spectrum may look different because the top and left margins, if present into the monitor window, are removed. If you want to preview into the monitor window the final inset, exactly as it would appear, reduce or remove the margins around the main plot.
An inset can't be manipulated directly, but can be promoted to the status of main plot. With the main plot, you know, you can do all sorts of manipulations. Press 7 or 9 to promote all the insets, one at a time, to the status of main plot. The old main plot goes into a dormant state (it's just another inset), until it's promoted back to its original status.
To verify which is the main plot, press 8.
A colored frame appears around it. Press 8 again to hide the frame.
The framed inset can be deleted with View > Remove This Plot. If you hide the frame, the same command deletes all the other insets.