Answer

Only AC works with transformers i.e. DC does not.
 Step up = increase in number of turns in coil = increased voltage but decrease in current. Ratio of voltage increase = ratio of current decrease e.g. if voltage increases by a factor of 10, the current will decrease by a factor of ten.
 The opposite is true for step-down transformers i.e. the voltage decreases and the current increases in the same ratio or by the same factor.