Building muscle is all about a balance diet and exercise. Protein is the key, like Black Wolf, Kasperl, and Goober 5000 pointed out. Calorie and the type of food you take play very important roles too.
You should have breakfast. Start doing that if you have not done so and try not to skip it.
1) Suggestion for breakfast: 1 serving of protein (such as egg, peanut better, cheese, nuts), 1 serving of whole grain carb (toast, cereal), 1 serving of fruits (citrus fruits or melon) and something to drink (tea or coffee).
2) Suggestion for lunch: 1 serving of protein (meat like steak, pork or chicken, fish), 1 serving of carb (rice, pasta), 1 serving of fruits and something to drink.
3) Suggestion for dinner: 1 serving of protein (meat like steak, pork or chicken, fish), 2 servings of veggies, 1 serving of fruits and 1 serving of ice-cream (a treat for yourself for eating well today).
I prefer tea to coffee because I don't like the taste of coffee and I think tea is a bit healthier choice. For protein, fatty fish (e.g salmon & tuna) and chicken are better than red meat. Do watch out the amount of fatty fish you eat though, because they tend to contain higher level of mercury. Have small snacks such as apples, and nuts between meals if you like. The term 1 serving usually means one cup. In some occasions, it means pieces or slices.
Last but not least, I think a 30 minute to an hour workout a day will be good enough. Swimming is a good workout if you know how to swim and have access to a pool.
I think that's pretty much it.