First you got to set yourself a goal. That goal is exactly why you want to go to the gym.
Do you want to really do bodybuilding ? Then you will need additives as the body of a bodybuilder seldom grows natural,
Do you want be able to lift a lot ? That requires a different way of training, Watch the Olympic and you will see that the champoins weightlifting look very different from bodybuilders.
Do you want overall strength ? That requires much more than lifting alone, you may want to take up some side sports to not just build muscles but use them as well.
Be careful in how you develop your body. While you are young it is easy to get a good shape, but it is also easy to make yourself used to vast quantities of food. In a couple of years, you will not want to spend so much time in the gym, and you will have to change your habits, or grow incredibly fat.