If you're calorie counting?
How do you know how much to count? Total calories?
Count calories per serving? Which?

It is more than counting calories per serving as a serving of broccoli has less calories than a serving of chuck steak. But you knew that. Also you need to calculate your BMR, which is not hard to do.

There are some online helps for learning how to count calories:

Calorie Calculator - Calorie Counter and Fat Calculator To Count Calories and Fat Grams in Your Diet.
Weight Loss - BMR - How Many Calories Should I Eat - How to Calculate Caloric Needs - Basal Metabolic Rate Forumla
How Many Calories Should I Eat - How to Calculate Caloric Intake - Count Calories to Lose Weight - Losing Weight by Cutting Calories 2
Calorie Counter Database - Free Online Diet Program

This is to a free online diet and exercise journal: Calorie Counter - Free Online Diet Journal

All I know is when I was on a diet it was 1200 calories a day.

Count the calories for one serving, if you can figure out how much your eating, like if a portion is 3 ounces of steak, look up what the calories are for that 3 oz portion. To count calories correctly, you'll need to be really paying attention to serving sizes. If the bag says 9 chips are 200 calories, you need to eat 9 chips, otherwise, start adding on more calories. The most important part of watching your calories is Portion Control, smaller portions, read nutritional labels,most foods tell you exactly how much of their product one serving is, stick to it and don't go back for seconds, if your counting calories. Also counting calories won't do you any good if your eating the wrong foods, fried, fatty, fast, sugary, salty foods are the wrong calories no matter how perfect the portion size.

With my weight loss, I watched calories and fat grams. Carbs were not a huge issue. You have to figure how many calories go in and How many calories go out through excersise

I love this site Free Calorie Counter - Calories Burned, BMI, BMR & RMR Calculator

It helps you count how much you consume as well as how many you burn doing all sorts of exercise and household chores, too.