Buy low, sell high, is the answer you'll get from a savvy veteran. If you buy something at one price and sell it at a higher price, you make money. If you buy something at one price and sell it at a lower price, you lose money. Traders around the world expressed their lack of confidence in the dollar by selling it and buying the Deutsche mark and Japanese yen. It's merely a matter of personal choice and perspective.
Most currency trading is short-term.
CME currency contracts are physically delivered four times per year - in March, June, September and December. Like the great majority of futures contracts, currency futures are usually offset in this way. The downside of this tactic is that the trader is no longer in the market, even though the underlying reason for the trade may still be valid. Thus the trader has transferred, or rolled, the position forward and is able to hold it for a longer period of time. Generally, a trader would do this when he or she felt that the market would eventually move in favor of his or her position.