Soy sauce has a real unique taste: it’s salty and a little sweet. When you go to a Korean grocery store, you’ll find that they stock many different kinds of soy sauce, usually without English labels. Personally I always use jinganjang (진간장).
This style of soy sauce was introduced from Japan and it’s relatively new to Korea, unlike traditional gukganjang (국간장 or “soup soy sauce”) which has been used for thousands of years. Like soup soy sauce, “regular” soy sauce is made from soybeans but the process is totally different, and the resulting soy sauce is darker, less salty, not as strong, and a little sweet. It’s better suited for everyday uses as a dipping sauce or a light flavoring agent, not to flavor a whole pot of soup. It’s too dark for that anyway – soy sauce for soup should be light in color so it doesn’t influence the overall color of the broth.
I remember when I was a student and soy sauce first gained popularity in Korea: I used to have a quick breakfast by mixing rice, soy sauce, and a bit of butter before rushing out the door!