The parts of speech explain how a word is used in a sentence.

There are eight main parts of speech (also known as word classes): nouns, pronouns, adjectives, verbs, adverbs, prepositions, conjunctions and interjections.

Most parts of speech can be divided into sub-classes. Prepositions can be divided into prepositions of time, prepositions of place etc. Nouns can be divided into proper nouns, common nouns, concrete nouns etc.

It is important to know that a word can sometimes be in more than one part of speech.

Source: https://www.grammar.cl/english/parts-of-speech.htm