Q: What areas do the treadmill target on your body?

A: Treadmill is primarily a cardio exercise. That means it carries benefits for your heart and can also assist you in losing fat from all over your body (the big asterisk here is that you should not rely on cardio alone to lose fat. See this for an explanation of complete fat-loss program). Treadmill will not build up any of your muscles to any significant degree with the possible exception of calves. Your upper legs may gain a little bit of mass if you've never done cardio or weight training before, but it won't be much.