The main difference is that public speaking is structured better, and often prepared earlier. Public speakers will often be more formal with an audience than someone they are having a plain conversation with. A conversation normally is just random subjects.
Either way, both are used to inform, entertain, etc.
Dr. Lanyon has learned damaging new information about Dr. Jekyll. I know this because after Utterson asks if Lanyon has seen Dr Jekyll, his face changes and he says he never wants to see him again.
The subordinate clause is "When the delivery man arrives" because 1. it is introduced by "when" and 2. we can ask question to the main clause about this one.
