Start by learning about nutrition, calorie requirements and meal planning. There will be no benefit to exercising if eating is out of control,
After eating is under control begin learning about, planning and doing strength training and cardio workouts. Exercise is necessary to have a lean tone body, However, the gains in muscle size from natural bodybuilding vary greatly and are very limited for most people.
After nutrition and workouts are under control start learning about supplements, realizing that many are useless but some may be beneficial.