Please suggest what foods are good to eat for someone who is working out and gaining muscle?

Protein, Carbs +: To build muscle with exercise, you need to supply your body with enough protein and fuel to support your body's daily needs (to keep your brain thinking, your heart beating and your lungs breathing), as well as the additional demand for fuel by exercise. You need a balance of protein, carbs and healthy fats for maintenance and additional protein in particular to build muscle, plus carbs for fuel.

Real foods, LowMod C: Muscle has higher protein content than most cells: the actin & myosin contractile machinery within, along with the thousands of other proteins & fats necessary for animal cell survival & function. Red endurance muscle burns more fat than sugar (e.g. Heart muscle ~98% fat). White, quick twitch low-endurance muscle burns more sugar, less fat. Thus high natural fats & proteins, low to moderate carbs.