Well your goal is somewhat flawed. You need EXTRA calories to build significant muscle mass. You need a calorie shortage to burn fat effectively.
That said, you do NOT need any supplements. Supplements 'supplement your diet'...if your diet already has enough protein, vitamins, etc...there's no good reason to supplement.
Many of us just find it convenient to get some of that protein, with very little fat or cholesterol, from a protein powder.
Whether you need 1 scoop, 2 scoops, or 4 scoops...depends on your current goals, your body, weight, age, and macro intakes that are specific to your needs.
For the record, the oak himself Arnold Schwarzeneggar used to down a quart of milk for his post workout meal.