First things first, steroids are not a magic solution for anything. Yes they do work, but they work only as much as you allow them to. Without proper education in them, they're not going to work as well as they could if you really knew what you were putting into your body. And without the intimate knowledge of how your unique body responds to training/eating/other-supps/etc, which only comes through a few years of experiential trial-and-error, you also won't be able to best use steroids to your advantage. If you're 20, spend a year or two really working on strength-training and developing a strong core (via compound lifts), and then a few more years really learning the ins and outs of natural bodybuilding. If you do this all right, you'll seriously plateau around 25, which is when you can use steroids to get to the next level if you feel mature enough to handle everything that comes with them. Don't rush this. It's a lifestyle, not a summer project.
Weight-gain is hard for a lot of people (especially if you eat well), but it's not impossible. You just have to really be committed to it (eating can be way more of a challenge than the actual work done in the gym for many reasons - one being that you do it every single day, all through the day). But here's basically what it amounts to. All food/drinks/supplements contain an amount of calories. You might eat, on average, 2500 calories per day. Now what you have to do, which can only really be done through a few months of experimentation, is to find the amount of calories you need to eat to maintain your bodyweight at your given activity level. So if you're a 180lb male and you exercise for an hour per day and do a lot of walking, you might need to eat 2500 calories per day to keep seeing that 180lbs (plus or minus one or two) per day consistently. If you eat that much, you stay the same weight. No gains, no losses. Make sense?
Okay, so it's really just as simple as this. You take that equilibrium caloric intake and you add 300-500 or so calories to it per day. This is called going into a caloric surplus, and you are "bulking" (subtracting calories would be a caloric deficit for "cutting"). Only 300 or so, you don't need to eat yourself out of house and home. Too much food is hard on the wallet, will add unnecessary fat, could result in stretch-marks and loose skin when you switch to cutting, and can get too mentally exhausting. 300-500 additional calories is about what you'd need to gain .5-1lb per week, which is more than enough of a pace for a healthy bulk. If it averages out to 3lbs a month and you bulk over the winter, you can easily put on 20lbs before you cut. With the gained muscle from the bulk, you might end up 3-5lbs heavier at the same bodyfat percentage once you've completed the bulk-cut cycle. Don't believe any of those ads that tell you that you can get 12lbs of muscle in a few months without steroids. It's bullshit; gaining 3-5lbs of lean muscle mass over the winter is more realistic. And good. Do that every year and in 5 years, you've really gotten off to a great start before ever hitting the juice.
As for how to eat the food, some people will tell you to eat 6-8 meals of the same amount of calories around the clock. So for a bulk at 3000 calories per day, you could have 6 meals of 500 calories. I don't do this, because my life is too busy and inevitably I cannot follow something like this to a T. I do write down the calories (and protein) in everything I eat in a journal, though, and it helps me keep a pace. As long as I meet my quotas for the day and don't end up shoveling food down right before bed to get there, I consider it a successful eating day. Don't eat shit food, but you don't have to eat super healthy on a bulk. Go out for wings, eat a pizza now and then. I am more comfortable "cheating" with foods high in protein. If you're really struggling to get the calories you need in, you can buy a weight-gainer from a health-food store and treat it like a post-workout shake.
As long as you can fundamentally get down the idea of calorie manipulation about your maintenance intake and have the discipline to eat that everyday, you will have direct control over your weight. It might seem like a lot of food at first, but the more you eat, the hungrier your body will get. Some of the other guys in the forum might be able to suggest products that stimulate appetite as well. Lastly, don't use any drugs or alcohol unless you have willpower of steel and can keep it extremely isolated. Because even if you can still go to the gym while you are using, it will fuck up your diet. Been there, done that.
Don't overthink it, but do keep it in the forefront of your mind. There are a lot of guys who train and train and train but never get to where they want to be (and say things like "I just have bad genetics"), when they're really selling themselves short for not thinking about this all like a science. We've all got the potential.
