warn / worn are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
warn: (verb) notify of danger, potential harm, or risk. (verb) admonish or counsel in terms of someone's behavior. (verb) ask to go away. (verb) notify, usually in advance.
worn: (verb) be dressed in. (verb) have on one's person. (verb) have in one's aspect; wear an expression of one's attitude or personality. (verb) deteriorate through use or stress. (verb) have or show an appearance of. (verb) last and be usable. (verb) put clothing on one's body. (adjective) affected by wear; damaged by long use.
warn: w·AO·r·n
worn: w·AO·r·n
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)