Your front and back matter are all the pages you put in your book that aren’t the text of the book itself. These are different for ebooks and printed books, so you need different versions of them for each type of format you are creating.
At the front of the book you could have the title page, table of contents, a dedication, copyright info, maybe a list of other books by the same author, or some great review snippets.
After the book you often have a note from the author, thanks, a more extended copyright info, links to social media. This is the perfect place to ask the reader to do something: a call to action here could be to order the next book, review the book, or sign up for the authors newsletter. Which you have first depends in which is more important to the author.
Some authors include teaser chapters of other books at the end, though Amazon especially is clamping down on this after issues with book stuffing on KU.
The best way to find out what to include is to look at other indie books in your genre and see what other authors have included and how they did it. You can then make your own versions, and over time you can change them as you have new books, or want to change how you present things.