Magic cannot help you with this. Just eat healthy and consume a bit more calories than you usually do. However don't go out eating a bag of chips, burger and fries everyday. That is unhealthy fat and you don't want that. Eat healthy fats such as avocados, peanut butter and nuts. Here is a link that should give you a list of all healthy fats and the unhealthy fats and some other things you should know in the process of gaining and losing weight:
If not then go speak to your doctor or do a research on your own as to what is good and bad for you.