Left: Chinese Soy Sauce (aka jin-ganjang)
Right: Korean Soy Sauce (aka joseon-ganjang)
It took me awhile to figure out the difference between these two types of soy sauce. I heard there are many more kinds in the market, but for my level of cooking, I have only used these two so far. The more familiar kind in western culture is the Chinese soy sauce on the left.
The very difference between the two, is the taste and its use, and of course the origin. Chinese soy sauce tends to be darker in color and sweeter than Korean. Thus, it is used for seasoning casserole, Jjigye (dense soup), or as a dipping sauce for sushi. Korean soy sauce is still dark in color but slightly more transparent than Chinese and contains more salt in it. Thus, it is often used to season light-colored soups and as salad dressing.
As many people know or have guessed, soy sauce is a byproduct of making (fermented) soybean paste, or vice versa... I don't recommend making a soy sauce on your own. I've seen once grandma makes soy sauce at home, and I have to say, it stinks really bad. I cannot imagine people today making soy sauce in their apartment homes. Their telephones will be ringing all night for complaints from neighbors. Home-made soy sauce is only the reminiscence of old times.