Astrology has oodles of ways to forecast upcoming trends in your life. However, sometimes it's helpful to look at your chart and see why certain things are happening right now. Depressed? Ambitious? Obsessed? If you're acting in a way that seems totally unlike you it could be due to your progressed Moon.
Your natal chart is not static. It changes over time and the best way to illustrate this is through progressions. Basically, progressions involve moving all the planets in your chart forward by a certain number of degrees per year. There are different ways of doing this but for simplicity's sake I'll focus on the progressed Moon.
Your Moon represents your emotional state so it makes sense that as it moves (progresses) through the signs your emotions will change. Very roughly, it moves about 12 degrees per year and often heralds major life changes. For example, if your progressed Moon is in Pisces you may feel hypersensitive, dreamy, withdrawn or depressed. You could feel like you're swimming through molasses until your Moon moves into Aries. Voila! The Sun has come out and you're buzzing with energy. I've seen people become obsessed when their Moon progresses into Taurus (it's a fixed sign and is ruled by Venus). Absolutely nothing can budge them from their fixation but when their Moon moves into Gemini they realize (Gemini is ruled by Mercury) how crazy they were acting.
Bells can go off when your Moon moves over one of your natal planets. If it hits your Sun you can feel ready to move onto the next phase of your life (depending on what area of your chart this takes place in). You'll feel it when any sensitive point in your chart (occupied by a planet, angle, node, etc.) is hit by your progressed Moon. Now, my explanations are very simple but if you want to know more, Cafe Astrology has a nice, straightforward article. For those who want to dig deeper, there's this article by Amy Herring.
Don't worry about trying to calculate your progressions. Astrodienst will generate a progressed chart for free. An exact birth time is helpful for this one (since the position of the Moon can vary by degrees depending on what time you were born). When you look at your progressed Moon, remember that it represents what you feel like doing. Although it may seem as if you have no control, you really do. After all, it's your Moon.