Between the trachea and the esophagus is a flap of tissue that closes when you swallow what is the function

It is called the epiglottis. When you breath is folds over the esophagus so you will not get air in your stomach, but when you swallow it quickly flips and fold over to the trachea. So your food will slid right down the esophagus and into your stomach. Also you know how when you hear someone cough and they say it went own the wrong tube, it actually means it went down the wrong tube.