I like to demo this using this file: http://www.cwoodcock.com/Civil_War_by_Campaign.kmz
As you can tell, it's a Google Earth file, but I'll be moving it into a GIS after we look at it in Google Earth. You can download it to your computer, open it up in Google Earth, and then browse the file.
And here is the same file, plugged into a lightweight, online GIS environment (Esri's ArcGIS online): http://arcg.is/1CPHCyY
So: Is GIS just the same thing as Google Earth? How is it different? Do we care about the differences?