hmm..there are quite a few modes for flash, ttl, auto, m.
for ttl, the flash takes aperture and iso reading directly from the camera. the flash will fire, bounce off target, goes thru lens and hit sensor. once sensor sense enough light, it will cut off flash.
for auto flash, u will need to set aperture and iso setting manually on the flash. the flash fires, bounce off target, goes back to sensor inside flash. once flash sense enough light it will cut off flash.
for manual, u calculate and set the power of the flash yourself, and then shoot.
most flash will be able to do auto flash, but u will need to set the aperture on the flash for it to work properly. skip manual flash, waste of time.
my advice, pick up a sb-600. not too expensive at ard $360+ new(considering a used sb28 cost $250, anything similar is still in the $200 range used), it can do everything u will ever need.
~MooEy~