Open Nov 4, 10am-4pm. It took me about an hour to try the things I was interested in; but there was more to try for the real enthusiasts. (also open today Oct 27 until 4pm, but I bet you're reading this too late.) Enter SF City Hall on Grove Street. Once inside, look for "PW Training" or "Poll Worker Training" direction signs to find the elevator. Ride elevator to the 4th floor. Tell the nice greeter that you don't have your poll worker instructor manual and she'll give you one.
If you're suddenly curious about election machine security because of recent Texas debacle where Hart "eSlate" machines switched users' votes, the "bad" news is that SF doesn't use those machines, so you can't watch one get confused. But you can ask some knowledgable folks about how to check a physical security seal and things like that.