A saved revision is created by clicking the STAR button however they are periodically created too.
To access a saved revision add the number of the saved revision you would like to see IE To export the text: http://beta.etherpad.org/p/test/2/export/txt
Change the number IE 2 in this case to 6 if you want to access the sixth revision.
IE: http://beta.etherpad.org/p/test/6/export/txt