Hey, I have a question
I see that you are 18 years old. Being that skinny is just normal for your age for many guys. I was that skinny at 18. I did not change any until my mid 20s. (1).So number one thing is be patient. (2).Number two is to learn as much as you can about fitness, lifting weights properly, power lifting, nutrition, high reps with low weights vs low reps with heavy weights etc. Go to YouTube, many different muscle magazines, Google etc for information. (3).Number three please keep a log of all your exercises that you do with weight and reps. This will help you to know what weight an exercise needs to be set at. It will help show you your progress. You may not look any bigger but the log will show that you are getting stronger which is more important. (4). After a good work out, shower at the gym. Towels are to sit on or dry off with but never to cover up. Be healthy, get stronger and stay nude.
Men mature differently than women and some are later in developing muscle mass. It seems unfair at 18, but later in life you will be muscular and lean while others may have become overweight and flabby, and then you are ahead. In the meantime, I agree that building the gross muscles is best, including legs and core. The abdominal muscles very important in building further strength in your body, plus it gives you a solid emotional base: determination and courage. Get to know others in your gym by showing up on a regular schedule and you will have inspiration and advice right there! Good luck.