Jo Ann,
Put batteries in series and you add their voltage, 6+6=12. The
connection looks like this:
(neg. white)-----[- bat1 +]----[- bat2 +]----(pos. Black)
Put batteries in parallel and you add their current capacity, but the
voltage remains the same. Two batteries that can each provide 10 amps
for one hour at 12 volts can provide 20 amps if connected in parallel.
The connection looks like this:
(neg. white)----[- bat1 +]----(pos. black)
|_[- bat2 +]_|
Hope this helps.
Best Regards,
Jim