I understand that such power is used instanteously as soon as it is
generated.  But demand at a given moment must be constantly changing. 
So somebody turns off a light or shuts down a motor. What happened to
the power that would have kept that light or motor running had someone
not turned them off?  Can you stop generating suddenly-unneeded power
in, say, a nanosecond--or less?  I don't see how--even a nanosecond is not
instanteous  Or how does it work if suddenly more capacity is needed.
And I think that more power is needed to start a motor up than to run
it at a constant speed.  Which leads to the same question.

Can you direct me to a site or sites that really and clearly explain
this?  I hope so but I am pessimistic because so often the net does
not have such information--it is the kind of question (as are so many
questions I come up with) that you might find in a textbook or better
with a knowledgeable teacher.  If anyone feels similarly perhaps you
can commiserate with me over the loss of the Askme.com site.