Thank god for Wikipedia.
Dubeolshik is the most common Hangul keyboard layout in use in South Korea. Pressing the Ha/En key once switches between Hangul as shown, and English.
In contrast to Chinese and Japanese, Korean is typed the same way as Western languages. There are two major kinds of keyboard layouts: dubeolsik and sebeolsik. Dubeolsik, based on the QWERTY keyboard, is more commonly used. While Korean consonants and vowels (jamo) are grouped together into syllabic grids when written, the script is essentially alphabetical, and therefore typing in Korean is quite simple for someone who understands the Korean alphabet Hangul. Each jamo is assigned to a single key. As the user types letters, the computer automatically groups them into syllabic characters. Given a sequence of jamo, there is only one unambiguous way letters can be validly grouped into syllables, so this grouping is done seamlessly by the computer, with the result that Korean can be typed in the same way as English or any other alphabetical language.