An epilogue is found mostly in fiction books. This is a short section that concludes the end of the story. It might take place immediately after the events of the story or there could be a leap of years or decades. It can also be used to segue into another series of events that are covered in a sequel to the book.
In a non-fiction book, this section could be called the Conclusion. A conclusion wraps up any loose ends the book doesn’t address. It might talk about what happened to the people mentioned in the book later or if the events in the book predated or caused other historically significant occurrences.
Both an epilogue and conclusion are written as if they were part of the book. If the point of view is different than that of the main text, then this section is properly termed an Afterword.
The Conclusion or Epilogue should only be a page or two. If you can’t wrap things up properly at that point, either continue in a sequel or go back to the main book and add more chapters.
Assignment: Write the Conclusion of your book. Is everything summed up nicely? Are loose ends tied off? Will there be another book that continues the story? This would be the place to mention that.