Each word in an English sentence performs a function. Similarly, each member of a basketball team performs a function in their specific role. Each member of the 5-member team has a specific position. Each member must know the function of his/her position or role. Each member should perform the function in their role completely.
In the same way, each word in a sentence performs a unique function, and has a specific position or location in the sentence. Similar to the basketball team members, some words have more important duties for expressing the meaning in the sentence, and other words have minor responsibilities, they act as the glue. The order of words in a sentence is important for understanding the function and role of each word (Larsen-Freeman, et. al., p. 19). The more important functional words are nouns, verbs, adverbs, and adjectives. The words that help to structure the sentence are pronouns, prepositions, conjunctions, and interjections. The effectiveness of your speaking and writing skills depends on your appropriate use of words in their correct position.
Larsen-Freeman, D., Celce-Murcia, M., Frodesen, J., White, B., & Williams, H. A. (2016). The grammar book: Form, meaning, and use for English language teachers. National Geographic Learning, Heinle Cengage Learning.
PARTS OF SPEECH
These YouTube videos explain these 8 parts of speech.
I will add other videos in the future.