In the first part of this paper, sound system of languages that is of primary and crucial importance in language study is explained under the headings Phonetics and Phonology. The role of such knowledge in teaching correct pronunciation and therefore in communication is indisputable. In the second part, Morphology, another sub-field of language study is defined along with the related terms before emphasizing how word structure and morphological processes contributes to teaching vocabulary and reading. In the third part, Syntax, which studies the structure of the sentences and phrases in addition to the rules governing them is defined. How it relates to language teaching is also explained. In conveying meaning, words work together with the structure. Hence, in language teaching, whether explicitly or implicitly taught, the way how structures are constructed and the rules at work are necessary to teach.