I am 20 years old can i take pre workout or fat burner to build body?

Fat burner: Taking theses things is often counterproductive. Pre workout supplements/shakes/energy bars are often full of calories that you then have to burn off before your workout can cause any fat loss. Focus on eating lean meats and avoiding simple carbohydrates and sugars. A combination of cardiovascular and weight lifting exercises with lower weight with higher reps will tone your body in a healthy way.

Not Recommended: At twenty, you do not require supplements to build muscle or burn calories. These types of supplements are not recommended. Instead, I suggest you research ways to modify your diet, which can more safely increase the protein needed for muscle development, and decrease the amount of carbohydrates and fat consumed. Google The Mediterranean Diet, and see what dietary changes may make sense for you.