Hangeul is not an alphabet. It's an alphabetic syllabary. ㄱ is one character but it needs to be composed into a final glyph like 각, which require 2+ characters. 가, 각, 갉. 뷁.
Kanji (not to be confused with Hiragana or Katakana) are different because the characters are already composed.
Yeah I had a brain-fart earlier. I totally forgot about that. Typing hangeul is basically the same except there's no need to possibly choose different hanja/kanji. ...unless you press the hanja key after the glyph is typed but before moving onto the next glyph. (Usually F9 or F10, iirc Windows IME defaults to ctrl+space).
Kanji (not to be confused with Hiragana or Katakana) are different because the characters are already composed.