Starting off with shimano gears

I am completely new to multi gear bikes, the last time i rode a bike was in 1965.My question, what gear combination do i need to start off on level ground.If i try to back pedal just a bit, to get the pedals at 12 and 6 o' clock to get maximum leverage to start off, the gears won't let me do it.What combination will let me back up the pedals?Thanks,Mike