Pangu was the first being, and is depicted as a gigantic humanoid with long, black hair and a large beard.
As the myth goes, before Heaven and Earth existed, there was only a dark, endless order. Eventually, a comsic egg was born from this calmness. Inside, of it, there were two things: chaos, and Pangu.
After eighteen thousand years, Pangu woke up inside of this chaotic egg. Unable to move or breathe, Pangu broke the shell and was born into the universe.(In some versions, he uses an axe to break out of the egg)
After his escape, Pangu separated the heavy and light parts of the egg to create the heavens and the earth. He held up the heavens with his arms, and stood on top of the earth.
The light and pure heavens became yang, and the heavy, dense earth became yin, thus forming the concept known as yinyang.
Pangu held up the heavens for eighteen thousand years. As he did this, he continued to grow about ten feet per day. So too, then, the gap between Heaven and Earth continued to grow as well. Eventually, Pangu collapsed from exhaustion.
Pangu passed away during his sleep, and his body became parts of the world. For example, the sun and moon, rivers and oceans, and the mountains are all formed out of Pangu. You can read more about this below!