If I were speaking in person to you rather than writing this, you would have seen me bow to you along with the greeting, “안녕하세요!” (For spoken greetings in Korean, see this post.) This tradition is definitely something you should learn if you ever intend to go to Korea or talk with native speakers in person.
As there are all kinds of bows and they’re used for different situations or occasions – for example, you don’t bow the same way to a coworker as you do to your parents on New Year’s Day – it’s a good idea to know the difference. Also, there are some people you probably wouldn’t bow to at all – like your really close friends. Do you shake hands with your best friend each time you see them? Unless you have a super awesome secret handshake that involves dancing, eyebrow wiggling, and complex hand movements, you probably don’t. Koreans don’t usually bow to their best friends either (unless they have a super awesome secret bow…?).
There are lots of great resources on the web that provide pictures, videos, and explanations of what each type bow is, when to do it, and how. Why not greet people properly in Korea? Look at these articles and videos to learn how.
Great pictures and explanations of the do’s and don’ts: http://blog.korea.net/?p=2622
Scroll down and read the Etiquette and Customs in South Korea (Meeting Etiquette): http://www.kwintessential.co.uk/resources/global-etiquette/south-korea-country-profile.html
Also check out the other etiquette tips that Kwintessential mentions – they’re extremely useful for anyone going to Korea or interacting with Koreans!
Some extra articles to check out:
KoreanClass101’s explanation and demonstration video in Korean with English subtitles: http://www.youtube.com/watch?v=jNK_FAUAsmo
Eat Your Kimchi’s Simon and Martina share a clip of Korean Car Bowing: http://www.youtube.com/watch?v=6pGPDWStSe8