People might need to gain weight for a plethora of reasons. They might be under weight or they might even need to bulk up for a movie role or an athletic pursuit. There are many foods that help gain weight.
The foods that help gain weight are often nutrient poor. Many desserts and even candy can help people put on fat. However, this is not the type of weight that will be good in the long term because people might develop other health concerns, like liver problems.
Try to take a moderate approach and just eat favorite foods in moderation. This might mean having nachos one night and pizza the next. The goal though is to still get fiber and nutrients with each meal. Always make sure to get all the amount of the food groups in one day. It is important for health not to skip out on an appropriate balance of carbs, proteins, and healthy fats.