There are 5 ways in which characters can combine to form a syllable.
In all cases, if a syllable begins with a vowel, the character ㅇ is placed before the vowel. In this case, the character ㅇ is not pronounced.
1 vowel as in
A vowel followed by a consonant as in
A consonant followed by a vowel
A consonant, a vowel, and 2 consonants as in
A syllable is pronounced from top to bottom and then from left to right. The syllable 값 is read ㄱ ㅏ ㅂ ㅅ. It is not guaranteed that a syllable is pronounced how it is spelled. The pronounciation of Korean syllables may change depending on the preceeding syllable, the following syllable, or even based on the word's etymology.