The same thing drives a trend in the currency markets as drives a trend in the equity markets: people buying and selling. An upward trend, more buyers, a downward trend more sellers. Never confuse a market with economics. There have always been and always will be trends, birds trend toward the South in the Fall, people trend toward a direction very powerfully. Look at the bubble of the late 1990's. It was a powerful trend that made a lot of people very wealthy but it had nothing to do with economic reality.
If you want to know about trends, don't complicate the matter. Find a gauge of some kind, 20 day moving average, 55 day moving average, chart trendlines, etc.
Trend following is the simplest successful investment technique there is. But simplicity is not the same as lack of difficulty. The psychology of trend following is difficult. You'll be buying ridiculously high prices and selling ridiculous low ones, feeling like an idiot at times and losing a lot of money being whipsawed.
BTW, the currencies are some of the best trending markets out there.
All trading the individual gets involved with in the FX market is a game being traded around the edges of the market. When you make money you are on the right side of the current trend. The amounts of money that go through on the "real" currency market make it almost impossible for the individual investor to see a true price, and set the boundaries to a profit outside of their means even if they are right about what is going to happen. The only way to make money in trading FX is to be a bank or a lucky gambler. Take my advice stay out of it, I used to work on a desk moving about 1.5 billion USD/DMK a day.
As for bonds, it is an interest baring instrument. PMV may have changed today, but it is still worth what it was yesterday unless you are looking to sell it, but that is another game played by very different rules.