Create columns, make more if you snack a lot throughout the day.
Write the date and time for each meal or snack, and don't forget to add what you drink even if it's water.
Enter your first two meals of the day, measuring how much before you eat it.
Finally use a calorie tracker or app such as fitness pal, I like this app (available in the App Store) for tons of reasons.
Line up your calories by each meal, and total in the final column.