In this function, "in" typically denotes something is resting at a specific place. You could also say, "He lives in England." "In" is also used to note a specific occupation or function.
The word "in" is used as a preposition.
Examples:After dismissal, she got in her school bus. She let her friends in after they used the correct password.
As you can see in these two sentences, the word in is used as a preposition to determine a place or where the object of the preposition is.