Hey,
Im 14 years old.My weight is 35 KG and my Height is 5'6''.Im very skinny and thin.I want to know how to became a bit fat at least healthier.I eat quite well but it doesn't help.So what's your advice?

If you eat regularly and eat a healthy balanced diet yet are still very slim then it is probably just that you naturally have a very fast metabolism and you may possibly gain weight after puberty is over. You could try protein/carb shakes, not as a meal replacement but in between meals and see if it helps you to gain weight as well as doing some weight bearing exercises to increase muscle mass. The most important thing is eating plenty of fruits, veggies, grains and proteins to help the body grow.