is it better to exercise for a few days or exercise different parts each day? ive heard conflicting advicing from different people?

to lose weight and put on some muscle

everything is fine cept my stomach where has the most fat

As Lionforce said before me, I'm not a certified personal trainer.  I have done some research on the subject, but I would recommend that you also go and do your own.

Generally speaking, you lose weight through cardio.  Building muscle will help you burn fat because lean muscle will increase your metabolism.

There is no way to isolate the area that will lose fat first- your body will take the fat stores from where they are present as it needs them, and it won't consult you to find out where you'd like it to take from first.

That said, if your goal is to both burn fat and to increase muscle growth, it's best to exercise before a meal, particularly before breakfast.  The reason is that your body burns off some short-term fat stores (I forget the actual name for these) while you sleep.  Additionally, the body produces GBH when your blood sugar is lower, and this will help in the production of muscle.  You do want to be careful, though- be ready to eat something as soon as you finish your workout, and pay attention to what your body is telling you.

In terms of what to exercise, Lionforce is definitely spot-on.  You want to vary what parts you exercise and make sure you give your muscles time to recover.  Depending on how easily you put on mass, this may mean as little as 48 hours between exercises for the same body part or as much as 3-4 days.  I read an article by Shannon Pittman for serious hardgainers that suggested doing only two workouts per week, extremely heavy but low sets.  Most people can exercise the same muscle groups every other day, and that's probably where you want to start.

There's a book called _Super Squats_ you probably ought to read.