In English, we classify words into eight parts of speech: noun, pronoun, verb, adjective, adverb, preposition, conjunction, and interjection. These classifications are based on how a word functions within a sentence, not necessarily on the word itself. Think about the last time you looked up a word in a dictionary— remember how a single word could be both a noun and an adverb, for instance....
When a word trips you up as you write or edit a sentence, you just might have a problem with its usage as that part of speech. So, we will look briefly at each of the eight parts of speech to help you understand how the words on your page are functioning. [excerpt]
Tenielle Fordyce-Ruff, Back to Basics II: Parts of Speech, 56(8) Advocate 68 (2013).