1. The first thing you need to know is that there are 2 types of stretching. Dynamic and Static. Dynamic stretching is more of a warm up and consists of quick movements. Static is a slow hold of a stretch and should be held for 30 seconds or longer.
2. The second thing you need to know about stretching is when to do dynamic or static stretches. Dynamic stretching is more of a way to warm up the muscles and prepare for a workout or intra-workout moves to keep the muscles and joint pliable. Static stretches are done at the end of the workout to help alleviate soreness and to lengthen the muscle after a strenuous workout.
3. The 3rd thing you need to know about stretching is why you are doing these. You do a static stretch at the end of your workout because if you were to lengthen the muscle before you train it you are likely to put the muscle out of range of motion it is used to and could cause an injury. Dynamic is done at the beginning of a workout to warm up the joint and muscles and prevent injury.