The three parts of a block
Every Korean syllable block has an initial consonant (초성), a vowel (중성) and sometimes a final consonant (받침, batchim). The vowel's shape decides the layout:
Why blocks always start with a consonant
A block cannot start with a vowel, so a silent ㅇ fills the first slot: 아, 오, 우. That is why the same letter ㅇ is silent in 아 but sounds "ng" in 강.
Final consonants sound simpler
Many different letters can be a final consonant, but at the end of a word they collapse into only 7 sounds: ㄱ, ㄴ, ㄷ, ㄹ, ㅁ, ㅂ, ㅇ. So 낫, 낮, 낯 and 낟 all end in the same "t" sound. See the pronunciation rules for more.
FAQ
How many syllable blocks exist?
Unicode contains 11,172 possible modern Hangul syllable blocks. Only about 2,000 to 2,500 are used in everyday writing.
Can a block have two final consonants?
Yes. Clusters such as ㄳ, ㄺ, ㄻ and ㅄ can be final consonants, as in 닭 (chicken) or 값 (price). Usually only one of the two is pronounced.