Weigh yourself
every day.
That's the first step.
Drink loads of water, loads of fresh fruit and veg, talk to your doc about fasting for a week to 10 days, exercise.
Diets are dumb - you need to change your lifestyle.
I'm 6'4" and weigh around 175lbs, which I can maintain with no sweat. Apart from the exercise-related stuff...
On the other hand, if you don't know where calories come from (as in "how do I avoid calories where do they come from"), I'd do a bit of research. Here, for example:
http://en.wikipedia.org/wiki/Calories