Nutrition is the foundation of any successful fitness program. You always hear things like nutrition accounts for 70% of your results, or 80%, or 90%. We don't know exactly how much nutrition contributes to body composition and muscle gain. And it may be a different percentage for each person. What we do know is that it accounts for the majority of your results and there is no way around it.
Nutrition is the foundation for a healthy body. You can workouts until you're blue in the face and ruin it in no time by the way you eat. The type and amount of food you eat will dictate the results you will get from your workouts.
When you choose your food you should look for high quality lean protein sources, fresh vegetables, good fats, and some fruits and other carb sources that aren't out to destroy your insulin sensitivity (make you fat).