철자 is the act of combine vowels and consonants to make a syllable. For example, we combine a consonant ㄴ with a vowelㅏ to make '나', which is a syllable. In Korean, a word needs more than one syllable.
철자법, also called 맞춤법, is a set of rules that are applied when you write with the Korean alphabets. The system of 철자법(its full name is 한글 맞춤법) is consisted of 자모(the Korean alphabets; the consonants and the vowels), rules on phonemes, rules on morphemes, 띄어쓰기(the word spacing) and others.
철자법 is very important in Korean because 한글(the writing system of the Korean language) was created under the format of the phonetic(alphabetic) writing as well as the syllabic writing.
English is a phonetic writing system, whereas Japanese a syllabic writing system. Therefore each language has its own rules on how to formulate and write words respectively.