Here's why the difference matters: Improvements in flexibility are specific to your body position and speed of movement. So if you do only static stretching — as most do — you'll primarily boost your flexibility in that exact posture while moving at a slow speed. While certainly effective if you're a contortionist, it has limited carryover to the flexibility you need in sports and weight training, which require your muscles to stretch at fast speeds in various body positions. That's why dynamic stretching is a necessary component of any program: It improves your "active" flexibility, the kind you need in every type of athletic endeavor.
Dynamic stretching also excites your central nervous system, and increases bloodflow, and strength and power production. So it's the ideal warm-up for any activity. And when you regularly perform both dynamic and static stretches, some of the flexibility improvements from one will transfer to the other.
Check out the following routines and try one for 5-10 minutes before your next workout: