The guy was 17... much easier to grow at that age, so it must be put in perspective.
Well the first thing would be to assess current food intake vs. weight.
For example write down everything you eat for 7 days. Including quantities. Everything you eat and drink that has calories/nutrients in it.
Then calculate how much calories you ate on average per day during those 7 days and see if your body weight stayed the same, increased (by how much) or decreased (by how much).
For example let's say you hate on average 2700 calories per day and your weight stayed the same it is safe to assume that 2700 calories allows you to maintain your weight. You would thus add about 20% for that number to find the average caloric intake you should consume for fairly rapid weight gain.
If you lost weight during the week then you'd have to bump calories even more. If you gained a little bit of weight you might keep it there or only bump it by 10%.
That's for caloric intake and YES it is important.
Then you select your food content. The first thing is to establish your daily protein intake... 1g per pound of body weight is normally enough. Then you must plan your peri-workout protocol. The proteins and carbs you consume pre, during and post workout. Here you should go with PLAZMA at 1 or 1.5 serving pre-workout and 1 - 1.5 serving during the workout. After the workout you could go with MAG-10 or SURGE WORKOUT FUEL.
The next step is to calculate how much carbs and fat per day.
Let's say (for example) that you need to eat 3500 calories per day. And 170g of protein. 170g of protein is about 680 calories. So that leaves you about 2800 to consume from carbs or fats.
For a hockey player I like more carbs than fats since carbs are a better fuel source for your sport. Fats are needed but mostly for health and proper functioning. A 65 - 35 carbs to fat split is a good starting point.
Since we have (IN OUR EXAMPLE... you'll have to find your own number) 2800 calories to spread that means 1820 from carbs and 980 from fats.
1 gram of carbs has roughly 4 calories so 1820 calories from carbs = 455g
1 gram of fat has roughly 9 calories so 980 calories from fats = 110g
THEN you have to spread these nutrients throughout the day. The two biggest carbs periods should be morning and peri-workout (or practice) (from PLAZMA). You should have carbs in most meals but the biggest portions should be at these two times.
Finally you have to make the best food choices. Except for peri-workout you want the most natural food sources possible. Two selection criterias: 1) the less ingredients the better (for example rice only has "rice" has ingredient, so 1... "rice krispies" has 15 ingredients... so rice is better than rice krispies) ... 2) the more natural the food is, the better.
There are other elements to consider but that's a good start.