All dogs stick their tongues out some of the time and this is normal.
It helps them to cool down. When a dog pants, moisture is created by their breath which evaporates and cools the tongue down, which cools the blood down, thereby cooling their entire body down.
Sticking tongues out and panting is dogs way how to cool down their bodies. They can not sweat, so they use other ways how to cool down and stick out their tongue is one of them.
They breath cooler air into their nose and breath out the hot air through the mouth.
Dogs also stick out their tongue, when they are stressed (just like people are sweating when they are stressed).