It is easy to get these three confused.
When I was first learning to write, I, too, got these mixed up and had no idea what my front matter piece should be titled. Was it a preface? A foreword? I had no clue! So, I did what most savvy people nowadays do: Search the internet!
And viola! My answer was found 🙂
I shall now proceed to pass on the knowledge I have learned to you and website links.
Basically, this is where you talk about why you wrote the book, and the circumstances that brought you to want to write it. So, the “how” and “why”. The “explanation”. You can also add in your credibility and experience in the topic of which you are writing. And/or acknowledge those who have inspired or helped you to create the book. It’s “about the book as a book”.
Typically this is something written by someone other than the author. An opening statement. It is a fellow author, or an expert in the book’s topic putting the stamp of approval on your book, and making you look good to potential bookstores.
It is doing just that: introducing the “content of the book”. This section talks about content and the presented themes. You can establish definitions and things that are of importance and will be used in the book.
I should add that the Preface and Introduction are similar to each other, and sometimes a little Intro gets mixed in with the Preface. This is fine, if you are only choosing to do one or the other in your front matter. However, if you have a Preface and also an Introduction planned, then make sure to keep the two separate and distinct.
I hope this has been of help and cleared up any confusion you may have been having! If you have any further questions, feel free to ask.