Simple. Your weight is because of the calories you’ve consumed. Period. Once you know how much you should be consuming in terms of calories, you can take control of your weight. This is no hocus-pocus. There is a mountain of science behind it. Use any online calculator to find this number. For your convenience, there is a free one on this site. Simply register and fill out your info – age, gender, height, current weight and last but not least, your goal (e.g “lose weight fast”). The site will instantly show you how much you should be eating in calories. At least for some time, start tracking everything you eat and drink and keep yoru calories under the number the calculator told you.
Next logical question is, how do you track what you eat? I personally find http://www.myfitnesspal.com to be the best one out there to track my daily intake. From achaar to zebra. MyFitnessPal has everything!
All this sounds very eay, but what do you do when you find that, your body starts telling you that it is hungry?! Do as I do. Drink water. It has zero calories. I keep a 1L water bottle next to my bed in case I feel hungry in the night. To keep your stomach fuller and more satiated, try and eat vegetables. They have fewer calories but make you feel fuller.
Very roughly speaking, if you identified “Lose fat fast” as your goal, if you track your calories (without cheating!), you should see a drop of about 500g (~1 lb) each week. Guaranteed by… science!