I looked up both words in a dictionary, but they both meant the same thing, "to sell".
I was confused because I've been playing around with verb conjugation, and one site told me that 売る was a godan verb meaning "to sell", hence naturally the potential form of this godan verb would be "売れる." However, it appears that "売れる" isn't merely a conjugated form of "売る” and is itself a verb, having its own conjugations....I'm confused
Maybe conjugations have conjugations?