I'm also a very skinny dude, and over the summer I got married and decided to start a work out routine and a serious diet. I started at 6" 125 lbs- yes you read correctly- but in 8 weeks I was 142lbs and gaining.
I'm getting over surgery(unrelated to my muscle/joints etc.) so I have unfortunately been out of training and lost a few pounds, but I'm starting up again and will be doing the same kind of routine.
I worked out off and on since highschool when I played sports and was never able to put on more than 5 lbs for any given period of training. This summer however I began a very serious diet with a fitness app on my phone that I cataloged EVERYTHING I ate and drank daily, with a goal of 3500-4000 calories daily. The app also identified most of the nutritional facts for each food I was eating so I kept track of fats, sugar, protein etc.
My target calorie intake included a shake mix I drank every day post workout in the evening, which I'll probably modify a bit this time around due to the sugar content, but it worked really well. Basically 2 cups of whole milk, 2 tbls of Peanut butter, 1/2 cup of vanilla/butter pecan ice cream, 4 scoops of gainer protein mix( I tried several kinds) and some granola. Its very high calories with good protein.
Throughout the day I focused on eating constantly; I don't naturally have a very big appetite so I worked 6 medium size meals into my routine, instead of three huge ones.
As far as working out goes I hit the gym 4-5 times a week for 45 minutes max, but made sure I was balls to the wall the entire time- no distractions, talking to people, etc. I tended to do isolated muscle groups, but after reading some more I'm going to start this time doing way more core body stuff(squats, deadlifts, etc.) and see how that works out.
So yea , tl;dr, You have to eat smart and have a very focused and consistent workout routine and it is very possible to put on a lot of mass, this coming from some geeky dude who has been underweight his whole life.
Cheers man, I'm obviously a newb at this myself, but I found something that worked prety well so I thought I'd share.