All you have to do is calculate how many calories you need for your body to function + The exercise that you do and eat more calories. 3500 extra calories a week = .4 pounds thats 500 extra calories a day then what you need. For me i need to eat 6 meals a day to put on weight. If your not underweight or unhealthy then its not really worth it, im doing it for soccer but if your just doing it for no real reason it will be hard to keep it up. Im not trying to discourage you but unless you have goals it wont work.

__________________
"I spent 90% of my money on women & booze... the rest i wasted" ~ George Best