Why one arguments is within quotes ("Books") and another one is not when display_list function is called?

All problems are best understood with practical examples, so let's make an example code.

The code

Books = ["Harry Potter and the philosophical stone", "Harry Potter and the dungeon of secrets", "Harry Potter and the prisoner of Azerbaijan"] 

#Let's make a function now

def display_list(display_name_of_book_series, the_list_of_books):
    print(display_name_of_book_series)
    print(the_list_of_books)

#Now let's call the function

display_list("Harry Potter", Books)

The points to take from the example are that

1) The double quotes ("") are used to make a string and anything inside the double quotes ("") will be a string.

2) If anything is a string, it will be taken as it is like, literally, for example, if I put (aposkfj3474734''';;;>><<<<mn(sjsjd) [ a, b ,c,c,v,(polo)] into a string it will be as it is, a practical example;

A_string = "  (aposkfj3474734';;;>><<<<mn(sjsjd) [ a, b ,c,c,v,(polo)]  "

print(A_string)

#Output (aposkfj3474734';;;>><<<<mn(sjsjd) [ a, b ,c,c,v,(polo)]

So anything inside double quotes("") is untouchable. Strings are like a Black Hole it absorbs everything and anything, what if you want to put double quotes ("") in a string, the principle is very simple just put the double quotes("") into triple quotes (""") and you got a string.

example of string;

A_string = ( """The name of the book is 'Harry Potter' and the name of the character is "Harry" is noob""" )

print(A_string)

3) A variable is a name you give or assign to an object ( an object can be anything, it can be a string, a list, a tuple, a number, a function .....) in this case Books is a variable or name assigned to a list of book names. Variables need to be assigned to something otherwise they won't work. an example

#variable      # A string
Books       =  "Books"

4) The display_list function takes two parameters and then prints out whatever is passed in, in this case, I passed in "Harry Potter" as a string and Books as a variable

SO in a summary, regarding your question, the "Books" is just a string and it can be anything you want it to be you can call it "123455" and it won't make a difference because it's a string the Books without the double quotes "" is a Variable and has a value stored in it, so if you put in Book list the program won't be able to find the name Book list because the Variable Book list does not exist.