@mm2270, Thanks for the welcome and the response. I'm 90% positive that
I did not click on "install update" or some variation of that, but
instead clicked on "go to App Store" and as soon as I did, a window
popped up saying "Installing El Capitan..."...
Um, apologies for stepping into this space, but this web page was near
the top of my google search for how to prevent El Capitan from
installing. I am not a programmer or system admin (other than being the
"admin" of my solo macbook), so I feel a bit...
