Striders are short sprints that you can do before your run to wake your body up a little bit. If you're doing a speed workout or a fartlek or a hill workout, you can do these short sprints to help adjust your body to this increased speed, little by little. Also, at the end of your run at the end of a long run, you can do striders to wake your body up a little bit. After you're doing a long run your body gets a little sluggish, maybe your form starts to deteriorate a little bit.
But those striders force you to pay attention to your form so that you're using your whole body. You're using your arms. You're doing a quick turnover, and again, it helps you pay attention to some correct form. Pay attention, keep your head up, keep your chin down. Keep your torso open, engage your core, pump your arms. Pay attention to landing on the mid-foot. You've got to land on the toe, so you can push off and really pump your legs and work on your turnover. This will help your form in the long run, as it starts to become ingrained in your brain.