Simply track your food and exercise, and set your weight loss goal. The site will do the rest and you will be able to see how your eating is affecting your health program. It's easy. Don't worry so much about fat and sugar grams. This site has helped me lose 53 lbs!
Mostly, it is the awareness of health goals and what I eat that does it. I also like to get lots of Spark Points ( in the "My Trackers" part) The more points you get, the more you read and become more educated about health and weight loss/management. Daily, I take the quiz, poll, and trivia. I also read blogs and post comments for more points. REad recipes for more points. You will get the hang of it. Spark People rocks.