Here is a graphic from the WSJ showing how the Carry Trade works. Carry trading is one of the most simple strategies for currency trading that exists. A carry trade is when you buy a high interest currency against a low interest currency.
Although a little dated I do like this graphic of the Carry Trade from the FT. Very applicable to New Zealand and we have discussed it at length at AS and A2 levels of the CIE course. The carry trade is a popular trading strategy used in the forex market whereby speculators buy high-interest-rate-bearing currencies and sell currencies with low interest rates.