A noun is a naming word, a pronoun is used instead of a noun. An adjective describes a noun, a verb describes the action of a noun. An adverb describes the action of a verb, a conjunction joins two sentences.
Substantivo estas nomig-vorto, pronomo anstataŭigas substantivon, adjektivo priskribas substantivon, verbo priskribas agon de substantivo, adverbo priskribas agon de verbo.