The Edit menu contains the usual items relating to copying, cutting and pasting you would expect to find in most applications. Aside from Undo, which applies to almost everything, these operations generally apply to text fields in the application and to nodes selected in the network view.
The items in the Edit menu, aside from Undo, do not currently work on items selected in the 3D Preview.
As most people will be familiar with what the Cut/Copy/Paste/Delete/Select All items do these will not be discussed.
Undo: This item will undo previous changes. You can use the Undo History window, which is opened from the View menu, to see all the changes which can be undone.
Duplicate: This item will duplicate the nodes selected in the last used, or focused, network view.
Group: This item adds the nodes selected in the last used, or focused, network view to a new group. The new group surrounds the selected nodes.
Ungroup: This item will ungroup the nodes selected in the last used, or focused, network view.
Preferences (Windows only): This item opens the Terragen Preferences dialog. More information about Terragen's preference settings can be found here.