Dude, whatever you do dont skip out on breakfast. this is the most important meal of the day. when you wake up in the morning your body has drained all the nutrienst out of it and you need to restock. eat lots of carbs and protein at breakfast. I would recomend oatmeal and eggs. take in 25% of your daily calories at breakfast. eat 6 meals a day. eat good healthy foods only. you dont want to gain fat. you want lean mass. eat healthy fats found in fish, nuts, seeds peanut butter. you never said if you train or not but if you do make sure you have a post workout shake with lots of protein and carb. also eat lots of pasta, potatoes, white breads, steak or lean ground beef, chicken, white rice. these are all mass building foods.
you gonna have to post some stats. like your age, length of training, stuff like that. that way we can give you better advice. if you have any other questions just ask! take care bro, and I hope this helps you out!