I'm not using any sort of computer program or tracking website myself, but I hear that they are wonderful. I just keep an old-fashioned notebook in my purse. The night before, I'll write down what I plan on eating for meals and snacks the next day. I keep the notebook with me at all times so I can log if I change something at the last minute. Usually, I try to stick with my meal plan.
As for how many calories I eat - I went to a website like
this one and asked it to calculate an estimate of how many calories I need to maintain my current weight. Right now I need about 2700 calories a day to maintain my weight. If you want to lose a pound, you need to eat 3500 less than what it takes to maintain. So, if you cut back your calories by 500 each day, you'll lose one pound that week. So, if I ate 2200 calories a day, I should lose 1 pound a week. 1700 calories should give me a weight loss of two pounds a week. However, you have to take exercise into account, too. If ate 2000 calories and burned 300 of those by exercise, then I'd still lose 2 pounds a week.
However, like I think has been mentioned before, it isn't exact. Everyone's body is different and will lose differently. I've been eating between 1700 and 1800 calories a day, and exercising for about 30 minutes each day (alternating cardio videos, walking, weight-lifting). I lost three pounds this past week. However, that won't be consistent. Next week, I might lose one or two pounds, or I might not lose anything. It goes up and down. Usually, I drop about two pounds a week, but I don't count on that. And I don't get depressed about it if I don't.
Anyway, I'm sure you'll do wonderfully once you sort out how your body responds to your new nutrition plan. Good luck!