What are the special functions the stomach performs?

The stomach produces acid that breaks down the food into simpler products. The low pH produced from the acid helps to kill of any bacteria that have entered into body from the food.  The stomach is also able to squeeze the food and churn it to help increase the brake down in to the simpler products. The chyme (broken down food) then passes in to the small intestine, this is where the nutrients will be absorbed.
Bile is secreted in to the small intestine this helps to brake down the fats. Simple sugars like glucose can be absorbed in to the blood and do not have to be broken down any more until they are being used by cells to produce ATP.