I have been having green tea for years now and it hasn't really helped me personally with weight loss. Basically, if you eat junk, don't workout and start having green tea, you won't see much of a difference.
Green tea is a thermogenic which means it raises your internal core body temperature which in turn raises your metabolism meaning you'll be burning more calories. Best way to take it for weight loss is in capsule form twice a day, midmorning and mid-afternoon. However if you have trouble sleeping make sure you don't take the second tablet too late in the day.