When I use 'Book' it's returning nil and I believe it should be returning something else

Okay, maybe I'm not understanding this completely. But when I use the Book struct in a constant, it is coming out as nil. Below is my code, and from what I understand, it should return 'Game of Thrones' as the title, and 'George R. R. Martin' as the Author. I'm obviously doing this wrong, since the I'm getting an error saying there's too many arguments. I understand there is too many arguments, but what I don't understand is where then, is the dictionary supposed to be created and used? I've been rocking it up until this point in the course, and I don't want to continue until I have a full understanding of what I'm doing wrong.

struct Book {

    let title: String
    let author: String
    let price: String?
    let pubDate: String?

    init?(dict: [String : String]) {
        guard let title = dict["title"], let author = dict["author"] else {
            return nil
        }
        self.title = title
        self.author = author
        self.price = dict["price"]
        self.pubDate = dict["pubDate"]
    }
}

let newBook = Book(dict: ["title" : "Game of Thrones"], ["author" : "George R. R. Martin"]);