First of all, you don't have to write them. In fact, if you force them, they can sour the book for the reader, especially the prologue, as it is the first chapter.
An hilarious mistake I saw multiple times actually is that people either mistake the terms or use them interchangeably. Prologues are at the beginning, Epilogues at the end. They are similar but not the same.
They are similar in the aspect that they are somewhat separate from the main story. Despite coming last, let's start with the epilogues, as I have to say the least about them. Epilogues tend to be set after the main plot, with time gaps between them and the last chapter. They are used to close a few last story threats, small ones, and more in a telling manner. They may be used to show what characters are up afterwards or as teasing for what comes next.
In my experience, you see more people writing prologues, than epilogues. At this point I want to add, you don't have to do both, just one, or none if you want.
Now, let's talk prologues. Like I said, these are a bit more common, at least in my experience. I think this is because you have a few more options and actual uses for prologues.
A big use for these is giving exposition that you can't really add into the main narrative. Maybe the prologue is set in the past or depicts the last moments of a murder victim. They are common for fantasy stories or Fanfics with heavy AU settings to give world building context. maybe to show the world is different because X exists. If X is shown in the prologue, ther author won't haver to add it into chapter one or two and ruin the immersion. But these exposition dumping prologues can go wrong.
They also can be very abstract and sprout many questions. Not directly asking questions, but making the readers independently ask them. Maybe the prologue depicts a character steals a jewel. Who is the thief? If it is heavily implied who it is, be it just their social status that should imply they have no reason to steal, why do they steal it anyway?
This could also be a 'In Medias Res'. Which means the story starts somewhere in the middle or near the ending, and abruptly stops. The first real chapter starts at the real start of the narrative or timeline. This has two functions. To make the reader wonder what is going on and to catch attention. What is more interesting, a story starting in a battle or prison break it or while the protagonist studies for an exam?
Despite being part of the narrative, the In Medias Res is still detached, as it is a piece cleanly cut out, put onto a different spot. This prologue type requires some plan of what you do, so pantsers, maybe do something else.
Fun fact, quite a lot of the newer Tomb Raider games start with Medias Res. So if you write a Medias Res, this would be Source material accurate feature in this fandom.
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Absolute Fanfiction Writing Advice
FanfictionI wrote and read Fanfiction for five years. In these five years, I learned many things. But these is still a lot to learn for me. To celebrate my five year anniversary, I want to collect said knowledge. While not all is stuff I learned over the last...
