Built-in graphics routines are very low-level. Most people who use graphics only directly use high-level graphics routines loaded into ISETLW from include files.
Reminder that once you start a graphics routine such as plot(), you have to type a q to quit that routine to enable again using the Execution or Text windows.
The current version of ISETLW does not allow saving graphs to disk or loading saved graphs from disk. Instead we recommend saving the Text or Execution window code that produced the graph(s), so you can later open that file and execute that code to reproduce the graph(s).