"You tie up loose ends and bring completion to all the threads you so carefully laid out for the reader's entertainment." (Beth Hill)
Everything in your story or book leads up to this point. The resolution is the final pages of your book that follow the climax or the final paragraphs of your story (also called the "denouement"). The resolution must fit the rest of your story. You should have it in mind when you start writing, laying the groundwork for what is to come. The warrior finds victory or defeat. The hero and heroine declare their love for each other. The detective catches the murderer.
Where should you start your resolution? Timing is everything: if you end your story too soon, you allow the reader no time for reflection; if you drag out the ending, the reader loses interest. How long should your resolution be? According to Beth Hill, if it is a novella, it should only be two or three pages. A series romance calls for a five page resolution. A political thriller will likely need more pages to tie up all of the loose ends of the story (http://theeditorsblog.net/2011/06/23/resolution-tying-up-the-ends/).
Ms. Hill states that the resolution should be "satisfying". It should "complete the puzzle, answer the vital questions" that the reader might have and give him or her a chance to digest the information. The resolution should slow the story down and reduce the tension. At the same time, it should "leave the reader wanting more".
Note: For examples of books with strong plot resolutions, visit http://www.publishersweekly.com/pw/by-topic/industry-news/tip-sheet/article/56760-the-10-best-book-endings.html.