Here's a breakdown:
Second Person:
* Directly addressing someone: "John, can you pass the salt?" Here, "John" is used in the second person because you are directly speaking to John.
Not Second Person:
* Mentioning someone in a sentence: "John went to the store." Here, "John" is in the third person because you are not speaking to John directly.
It's all about context! The grammatical function of a name depends on how it's used in a sentence.