for a skinny person the best way to gain weight is to up your carb intake as well as protein, if you dont have the energy to burn when you workout you're only going to be wasting your muscle cells. and also, if you're planning to lift weights often to help you gain weight, DO NOT overtrain, most people train one body part till they cant even move it anymore.. 9/10 this is overtraining, and can lead to a decrease in muscle volume and it will take a hell of alot longer to recover.