I'm a bit of a newbie myself, but here's what I did:
1. Under the weight tab, enter your weight.
2. Under the activities tab, choose your basic metabolism. (For instance, i chose 'Seated, some movement.") Then choose sleep as an activity, and enter how many hours you usually sleep a day. Then you can see how many calories a day your body burns. (So if it shows your body burns 2000 calories, if you eat more than than, you'll gain weight; less than that and you'll lose weight.)
3. At the weight goal tab, enter your goal weight and date. Then at the bottom of that page, look at the calorie restriction tab - that will show how many calories you need to spend a day (either through eating less or exercising more) to reach your goal by your goal date.
If your base rate is 2000 calories, and it shows you need a calorie restriction of 700 to meet your goal, you can either eat 1300 calories a day or do activities that burn an additional 700 calories a day, or a combination of calorie reduction and exercise.
4. Enter everything you eat into the food log.
5. Enter any additional activities you do into the activity log.
At the bottom of the food log page, you can look at the calorie balance tab to see how many calories you've eaten vs burned for the day.
Age 61, Height 5'9"
March 2010 145 lbs, Jan 2013 173 lbs
1st Goal 145 lbs 5/25
New goal 140