A sync cord came with my purchase and I plugged one end into the mic jack of the D5100 and the other into the extra hot shoe piece that came with the flash, which I've attached to it. But that isn't automatically syncing them. The manual and Lighting 101 both don't explain how to actually sync them once the cord has physically connected the two.
I thought maybe the mic jack in the D5100 wasn't the right one, but there isn't any other place in which to plug it. I tried to attach another extra hot shoe piece to the flash mount, but obviously that gets in the way and prevents the built-in flash from popping up and since I can't find any clear instructions for this process, I don't know if it's even safe to put the hot shoe there. Full instructions for how to do this set up, including the sync after the physical connection has been made? Please?