Your body responds to your food intake the most during your first meal of the day which makes it more important to what you first eat.
Insulin is a hormone secreted by your pancreas to control your blood sugar level. To lower your blood sugar, insulin will either store the glucose as fat or use the glucose for immediate energy. The presence of high insulin in your blood will turn off fat burning.
Carbs are chains of sugars and will secrete the most amount of insulin in your body. Fats are chains of fatty acids is more neutral to insulin so when you eat foods high in fat it does not raise your insulin level.
Carbs are a good source for immediate energy when doing strenuous activities. When doing activities such as sprinting and lifting weights, your body uses glycogen stores for energy. These glycogen stores are replenished by eating carbs that get stored in your liver and muscles. When it gets filled up there it will then use your fat stores.
A good strategy when trying to lose fat is to save your carbs for later meals so that you do not spike your insulin. This allows you to tap into your fat for fuel between meals. The carbs you eat in the later meals will not spike insulin as much and it will allow you to replenish your glycogen stores for use the next morning.