I’m reading Word Power Made Easy and here’s how it teaches to distinguish nouns, verbs, adjectives, and adverbs.
Nouns
A noun is a word which can be preceded by a, an, the, some, such or my. Eg: An egoist, Such asceticism, Some mysogynist.
Verbs
A verb is a word which fits into the pattern: Let us ___. Eg: Let us eat, Let us talk, Let us philander.
Adjective
An adjective is a word which fits into the pattern: You are very ___. Eg: You are very egocentric, You are very sinister, You are very gauche.
Adverbs
Adverbs are formed by adding -ly to an adjective. Eg: sinisterly, educationally, egocentrically.