Afterward is an adverb meaning (1) at a later time, or (2) subsequently. Afterword is a synonym of epilogue—that is, a short addition or concluding section at the end of a literary work.
Examples
CC Sabathia threw about 30 pitches of live batting practice this morning and reported afterward that all went well … [LoHud Yankees Blog]
Each book’s photos are accompanied by text from the subjects, with Elton John providing an intro and Kylie Minogue an afterword to the Shears book. [Dallas Voice]
Bill will also be on hand afterward to discuss ways to improve cycling in the community [letter to The Carrboro Citizen]
In the afterword to the 2004 edition of the novel, Donna Tartt calls the book “a masterpiece.” [National Post]
Rates would rise 8.2 percent again in mid-2012, and then 4.6 percent in each of the three years afterward. [Arizona Daily Star]
The book concludes with a lengthy afterword from Lessing in which she discusses the influence of Robert Scott’s doomed expedition to the South Pole on both this volume and The Sirian Experiments. [Locus Online]