I think part of speech is really important in writing and speaking, because it is like the foundation of English language. I have learned about basic part of speech since elementary school like verb, nouns, pronouns, and adjectives. The example in a simple sentence: I am studying, you are smart, and i love you. I learned about verb, to be, and how to speak english well. And then continue at junior high School. I have learn about interjection, Conjuction, preposition, and etc. Preposition It is like on, in, at, above, in front of, behind etc. And Begin to learn more and more about English at senior high School.