hi Al,
S and F are the Start and Finish of the windings, these are the phase sense of the 'ac' voltages.
If you have a transformer with two windings and you wished to connect the two windings is series, you would connect F1 to S2 and use the S1 and F2 as the output to the rectifier, etc.
To connect two windings, of the same voltage, in parallel you would connect S1 to S2 as one output wire and F1 to F2 as the other output wire the rectifier.
OK.?