Getting proper nutrition means eating the right quantity and type of foods for supplying essential nutrients to the muscle for growth and for the body to get enough energy that it will need during your bodybuilding training. As a rule you must be eating more calories (energy in food) than you're using up to put on muscle. The excess calories will be used by the body to build up muscle mass when you exercise.
However, you must optimize your caloric intake and weight training for maximum effect at gaining muscle with minimal fat gain. You see, if you don't use up excess calories with exercise to be utilized as energy or build muscle it will be stored as fat which you need to avoid as much as possible. Apart from sufficient caloric intake, another crucial function of the food you eat is to supply various nutrients needed by the body for growing muscles. They include amino acids from protein foods, glycogen from carbohydrate foods and fat foods also contain properties that releases testosterone and other essential hormones needed for muscle development.
The above is the basics of getting bigger muscles that you need to know about if you're planning to get a muscular body. Now that you've learned this your next step should be to obtain a good guide that'll show you step by step how to workout, eat and rest properly to start gaining muscle.