The difference between static and dynamic stretching is that static involves holding a stretch whereas during dynamic you are moving the muscles throughout the stretch. Both have benefits to exercise however it is suggested that you perform static stretches at the end of a workout as there is evidence that performing static stretching before exercise can hinder your overall performance. Dynamic stretches have the opposite effect, they are designed to increase blood flow to areas that you are about to train during your main session. You should include both forms of stretching for a more complete and effective workout!