I'm kind of new to basic electronics myself, but I think to convert from AC to DC, you arrange a series of diodes in a special pattern to get, first half-wave, then full wave rectification. I think it's called a "bridge rectifier" and on most schematics appears as a diamond pattern of diodes. You have to make sure the polarity of each diode in the diamond pattern is correct for it to work properly. After that you'll need a capacitor to smooth, or flatten, the waveform of the, now "positive only" waves coming out of the rectifier... That'll give you DC, with a bit of "ripple" in there because the flattening probably won't be perfect... Then going from a higher voltage DC to a lower voltage should be straightforward. Not sure if the higher voltage should be stepped down before or after rectification though, so maybe someone else will chime in on that...