Use the Edit menu on the main window as follows:

  Action      Function
  ------      --------

  Cut         Cuts selected text from the current command
              line and copies it to the clipboard.
              If selected text is anywhere other than
              the current command line, copies the
              text to the clipboard.

  Copy        Copies selected text from the window to
              the clipboard without removing it
              from the window.

  Paste       Pastes text from the clipboard to the insert
              point on the current command line in the
              command view.

  See the DECwindows Motif documentation for more information.