Skinny guys think that gaining weight is a very difficult task and a long process which may take months, but the reality is that with commitment and hard work you can gain weight and muscles within one month.
The first thing which is necessary is to change your diet so that you may intake extra calories which will help you in gaining weight and muscles. These should be rich in protein and nutrients rather than only fat, a professional diet should be followed after meeting with a professional trainer.
The second most important thing is that you should start working on your muscles under a professional trainer so that the extra calories are converted in muscles rather than fat and a big belly.
You should get proper sleep when you are in the process of gaining muscles, at least 8 hours of sleep is needed so that your muscles may relax and the proteins and calories can do their job in muscle building.