The next question is then, what constitutes a serving of each food group? The best way to get a feel for this is to look at various examples that constitute a serving. 

Carbohydrates
A serving of carbohydrates should contain about 15 grams of carbohydrates. Examples of this include:
Bread 1 slice
Tortilla, roll, or muffin 1
Bagel, English muffin or hamburger bun 1/2
Rice, pasta, cooked cereal, grits 1/2 cup
Ready-to-eat cereal 3/4 cup (flakes or round)
Pancake, waffle 1 (12cm diameter)

Fruit
A serving of fruit should contain about 15 grams of carbohydrates. Examples of this include:

Chopped, fresh fruit 1/2 cup
Grapefruit 1/2
Cantaloupe 1/4
Canned fruit 1/2 cup
100% fruit juice 3/4 cup
Raisins or dried fruit 1/4 cup

Vegetables
A serving of vegetables should contain about 5 grams of carbohydrates. Examples of this include:
Cooked vegetables 1/2 cup
Chopped, raw vegetables 1/2 cup
Raw, leafy vegetables 1 cup
Vegetable juice 3/4 cup

Protein
A serving of protein should contain about 15 grams of protein. Examples of this include:
Cooked lean meat, fish or poultry 60 - 90 grams
Egg 1
Peanut Butter 2 tablespoons, 30 grams
Cooked dried peas or beans 1/2 cup
Cooked dried beans 1/2cup
Nuts, seeds 1/3 cup

Dairy
A serving of daily should contain about 300mg of calcium.  Examples of this include:
Milk 1 cup
Yogurt 1 cup
Cheese 1 slice 30 grams
Cottage cheese 1/2 cup
Pudding 1/2 cup
Ice cream 1/2 cup

Fat
A serving of fat should contain about 5 grams of fat.  Examples of this include:
1 tsp vegetable oil
1 tsp butter
1 tsp peanut butter
8 ripe olives
1 tbsp salad dressing

Water
1 Glass of water