How Do I Kno How Much Calories Are In the Food I Am Eating

Well if the food you're eating is in a package of some sort, you can look on the side and it will tell you how many calories per serving. I also use nutriondata.Com for things like fruits and vegetables that I may not know the exact number of calories.

Try this website, its the best one I have found for calorie information:
Get yourself some good quality kitchen scales so that you can accurately weigh the food you eat as most people can underestimate their calorie intake by half.