It's impossible to gain 80-100 pounds of muscle in 6 months. By the best of all conditions you'll get 10-20 pounds of muscle weight, which are fairly good.
Just start to lift weights and go into an hipercaloric diet, start at 3,000 calories and add 100-200calories over time when you stop gaining weight. Eat a plenty amount of proteins, carboydrates and fat. You want good clean proteins (chicken and turkey breast, lean meats (beef, pork etc), milk, eggs, tuna, salmon, etc), complex carbs (integral pasta, wild/integral rice, oats, sweet potatoes), good fats (olive oil, salmon oil, flax oil, avocado, nuts in general) and plenty of fruits and vegetables. Water is essential, have at least 2liters per day.
Eat around 5-6 meals per day, and leave 3 hours between each meal. Time isn't an excuse. NEVER skip breakfast or dinner.
As for supplements, creatine and weight gainers will help you reach your goals. WHEY Protein is mandatory, no matter what. Have it as soon as you finish your workout. You can have homemade weight gainers, too, which tend to be superior to commercial ones.
Your weight lifting routine can vary, depends on your needs, but it usually goes like this: train a muscle and at least give 3 to 5 days of rest to that muscle. So you'll end up training a muscle once or twice per week. Change your routine schedule every 3-4 weeks. Give priority to complex exercises (bench press, squats, deadlifts, military press, barbell curls, rows, etc). And change the weight constantly. Stick to 8-12 reps for 3 or 4 sets, and use a weight that is challenging enough for you.
If you wanna get big, you have to eat big. Good luck bro.
"I think EVERYONE here on GW has to have cranked one out over Pulits or Trujin before. How's it feel, guys?" - Christophomicus <--Feels great, btw.