Why do we use books sometimes instead of articles? What is the difference between a chapter and an article, since they're about the same length? Why isn't an encyclopedia article considered a peer reviewed article, and why isn't an encyclopedia the same as a book?
Each format has a different function, different scope, different purpose. Know this helps you know where to start your search.
Every type of scholarly source has a specific purpose and scope, and knowing what each publication is meant to do will help you know where to start. The general types are:
A reference source is a very broad in scope and meant to be a starting point. It gives you a very general overview of a topic or person, and will often suggest books, articles, and primary sources. Some reference sources are peer reviewed, others are not; speaking generally, you should not cite encyclopedias or their articles as sources, but should use them as a guide to find peer reviewed sources.
Books (or "monographs") are the major medium for scholarship in history. Books are self-contained worked that provide background information and have a central theme or argument. Not all books are peer reviewed. For this class, books will likely be your starting point for secondary sources.
Chapters are about the same length as articles, but similarities end there.
Unlike Articles, which are standalone argumentative works, chapters are meant to be read within the wider context of a book.
Chapters do typically have an argument but also provide more contextual information than articles.
A chapter is a better standing point than an article if you're new to a topic.
Peer reviewed research articles, unlike books, are not meant to provide overview of a topic.
They are argument driven, and designed to focus on a very specific question.
Once you know a good amount about your topic, you can use article to address more nuanced aspects of your topic.
Book reviews are very short pieces that are included in academic journals, and the summarize & critique books.
These are Not peer reviewed article and should not be cited as sources.
They are, however, very useful by highlighting books you might find interesting.
Dissertations are weird. They are academic & scholarly, but not really peer reviewed.
They are as long as books, but more like articles in nature: very narrow, very argumentative, not usually a great place to start.
For this class you probably won't need to use a dissertation, and your professor may not want you to use one at all.
For later projects in your academic career, though, keep these in mind: their lit review sections are excellent, and for the most cutting edge research they may be the only sources.