Phonology

Phonology is the study of sound systems, or the sounds of language in context and the rules languages apply to them. It is related to phonetics.

Phonotactics
Phonotactics is the field of syllable formation, and investigates what syllables are or are not permissible in a language.

All human languages allow at least the syllable structure CV (Consonant-Vowel). Most also allow word-initial vowels.