How do I suppose to gain weight properly?

Need more info. How tall are you and how much do you weigh? If you are otherwise healthy but skinny. let it be. With age you will gain weight and look back fondly at this time when you could eat and not gain weight. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, low fat milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco or alcohol in any form. Practice safe sex.