Parts of speech are the different categories that words are grouped into based on their function in a sentence. The main parts of speech are noun, pronoun, verb, adjective, adverb, preposition, conjunction, and interjection. Understanding parts of speech helps us to identify and use words correctly in sentences. For example, nouns are used to name people, places, things, or ideas, while verbs show action or state of being. Learning about parts of speech can help us to improve our writing and communication skills.