Most streets in Seoul have no name. Yep, no name. If they do have a name, there is usually no sign and even if there was a sign, it would be in Korean and I'd have a hard time reading it anyways. (My Korean is getting better, but I have a LONG way to go!) Using street names and numbers is a very Western idea that has not been adopted in Korea yet, althoug there is talk of naming the largest streets in the coming years. so, traditional ways of locating things are used. Be prepared to feel a little confused. :)
Seoul is divided into 25 districts (gu) and 522 smaller neighborhoods (dong). Every building has an official number, but these numbers are assigned as they are built, not in the order they are placed in the street. So, building 27 could be between building 324 and 19. Nice, right? The building usually has its number written on in Hangul (the Korean phonetic alphabet).
So, a typical address lookes like 104 Itaewon-dong, Yongsan-gu. This means building 104 in the Itaewon neighborhood of the Yongsan district. But, you could wander around for hours and maybe not find 104 as there seems to be no ryhme or reason to why 104 is in its particular location. In fact, only postmen have maps with building numbers on it!
Many guidebooks, websites and things that we read give information about how to find a location based on its proximity to subway stations and exit. (Example: Take line 4 to Hyehwa Park, exit 2)What I try to do is navigate based on major landmarks, as the majority of places look just about the same (huge apartment buildings, markets, large expressways, tollbooths). Also, I check out the maps in the subway, as they will tell you what is located outside of every subway exit. When all else fails, look for another foreigner, or talk loudly about not being sure where you are, and typically a kind Korean who speaks English will come and ask if you need help. "Yes, actually I do." :)