«In the street» means you’re literally standing on the roadway where the cars would go.
«On the street» could mean you’re on the sidewalk and is probably a more common scenario. I would NOT say «I’m in 6th Street.» But I WOULD say «I’m on 6th Street.»
Native English speakers will always know what you mean if you mess this up, and they will never care. So don’t worry about it unless you’re a perfectionist.