Answer:
Eat your proper portions. And don't just eat junk food, because that is not healthy.
Step-by-step explanation:
To gain weight slowly, you should eat an additional 300-500 calories. To do it faster, consume 700-1000 more calories than you normally eat.
If you just eat small portions or just "healthy" stuff, then it is likely you will stay skinny as a stick. If you are wanting to have a little more meat on your bones, then this is what I suggest you do. It will be a healthy way to gain weight, and it's always important to put health first. But just because I said you eat more than your normal intake, that does not mean you have to stop exercising and/or you need to force yourself to pig out. That will be unhealthy.
-I hope this helps.
-No one