If you want to get big, you gotta eat. No getting around it. Eat, Eat. Eat whenever you can.
-Complex Carbs (Rice, Pasta, Grits, Oatmeal)
-Meat (Fish, Chicken, Ground Beef, Red Meat etc)
limit salts, sugars and excessive fats. Don't be afraid to get some fat in your diet, just don't overdo it.
To pack on weight in a reasonable amount of time you need to be getting anywhere from 3500-5000 calories a day.
Never skip a meal.
Get at least 8 hours of sleep per night
Limit Alcohol Intake
As for workout programs if your looking to bulk up. There is a workout regime called "West Side for Skinny Bastards" by Joe Defranco
get a decent Whey Protein, Fish Oil, Multi-Vitain, Joint Support, and if you want to pack on faster get a weight gainer powder. Up Your Mass and Cytogainer are the two best.
You could also use but don't have to- Nitric Oxide and Beta Alanine
If you're over 21 you could also use a testosterone booster but it's your choice.
Hope this helps