I am 18 years old my height is 170 cm and my weight is 48 kg so i need to gain weight by a healthy way?

Gain weight: You should eat a wide variety of healthy foods. If you have no food allergies to dairy , butter or peanut butter then those are good sources for calories. You probably are still growing so most of your calories are put into that. You will start to gain wait once you eat more calories then you burn .

Calories & prote: The addition of calorie dense foods such as nuts, whole grain pastas, raisins, whole milk, pure fruit juices, butter, avocado, and complex carbohydrates is a healthy way to add more calories to your diet. Lean proteins are also important. Good luck