Eccrine glands produce sweat. They are located all over, except in the genitals and areolas. The highest concentration of eccrine glands is in the soles of the feet, palms of the hands and the armpits. Armpits also contain apocrine glands which is why that area tends to be the first to let those around you know that you have been sweating/exercising since you last showered.
In humans, eccrine glands first develop at the beginning of the second trimester.
Eccrine glands help the body maintain a proper temperature in a constant and mostly imperceptible process known as thermoregulation. The evaporation of sweat on the skin's surface cools the body down in a humid place where the room temperature is high. During an emotional response, the eccrine glands around the palms and soles will activate moreso than the others.