A query letter is a request for a publisher to read your proposal for reading your fiction book and a book proposal is a proposal for reading your nonfiction book. A query letter is usually written after a fiction book is written and a book proposal is often written before the book is written. Since you have written a book of fiction, if you are going the traditional publishing route, you will be writing a query letter.
Of course, you no longer have to go the traditional publishing route. Many people are self-publishing or going through small press publishers or even doing what is called hybrid publishing which is a cross between traditional publishing or self-publishing. This post, however, is about how to contact a publisher or agent. Click here to learn how to contact a publisher or an agent.