There are eight or nine (or more) parts of speech, depending on what you read. Some authorities list nine parts of speech. Those authorities who list eight consider determiners (articles, quantifiers, etc) as adjectives. This site lists nine parts of speech.
To determine what part of speech a particular word is it must be looked at in the context of the sentence. Many words may be a different part of speech in different sentences. Look at these examples.
Mr. Elliot feels well. (Adverb).
She is not a well woman. (Adjective)
Well! What happened? (Interjection)
He dropped his hat into a well. (Noun)
An explanation of the differnt parts of speech in Englsih grammar– www.understandinggrammar.com