How Skinny Guys Gain Weight
The important thing to keep in mind is that gaining weight is about consuming more calories than your body can burn. If you are a skinny person, you probably either don't eat much, or you have a high metabolism. This will cover both issues.
High Metabolism
If you have a high metabolism, then you will have to try to outeat it. One way to do this is to be eating all the time. Eat about 6 to 8 good sized meals every day, starting with one right whenever you get up and ending with one right when you go to bed. You may want to even get up and eat a high protein or carb snack at midnight if you are still not gaining weight. Then once you gain all of the weight that you want, start easing back gradually on the calories at about half the rate that you added calories. You will drift down a little in weight, but you will stay up in your target weight range.
How to Eat More
If you don't eat enough, then you should probably start eating about 5 or 6 good sized meals a day, much like a person with a high metabolism would. However, your goal is to eventually desire food more often and to need more. Eventually, you should gain weight and be hungry more often. Start trying to wait between meals and see how much you can eat before you get full. Space out your meals so that they are pretty far apart and then gradually bring them closer together on a week by week basis. Eventually, try to eat two meals so close together that you only have to sit for fifteen minutes. Once you get that done, then you can combine them into one meal.
These take a lot of time and execution, but you can do it. Just follow the instructions and you will be able to get to that target weight that you desire.