أَخْبِرْنِي عَنِ الْإِسْلَامِ means “Tell me about Islam.” أَخْبِرْ is an imperative, نِي means “me,” and عَنْ identifies the topic asked about.
The visitor's broad question led to an organized reply about foundational religious acts. Effective questions do more than obtain information; they help the whole gathering see how a subject is structured.
For example, “What is Islam?” is a wide question, while “What are its main practical foundations?” asks for a specific part of the explanation. The scope of an answer should fit the question.