failable initializers and passing dictionaries. Code challenge

The instruction is:

In the editor, you have a struct named Book which has few stored properties, two of which are optional.

Your task is to create a failable initializer that accepts a dictionary as input and initializes all the stored properties. (Hint: A failable init method is one that can return nil and is written as init?). Name the initializer parameter dict.

Use the following keys to retrieve values from the dictionary: "title", "author", "price", "pubDate"

Im having trouble understanding why and how you would pass a dictionary through the init while also trying to define the initial self values. I could be misunderstanding the wordage completely or could be just off the mark. THe furthest ive gotten to workable code is:

struct Book {
    let title: String;
    let author: String;
    let price: String?;
    let pubDate: String?;

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

Thoughts?