Search engine: crawl the entire Internet and create an index. When you ask it a question it uses that index to point you to an answer among all the information it crawled.

LLM: crawl the entire Internet and train a model. When you ask it a question, it uses that model to spit out an answer. Worse than a search engine though, if it can't come up with a good answer it just makes shit up

Both use the same sources of information. Neither can produce a (correct) answer that doesn't exist somewhere in that information source