Let's start with prologues...
The first thing to say is that if you have no good reason to include one in your novel, don't.
The opening of a work of fiction is all about hooking the reader and keeping them reading - and prologues, however exciting or crucial to the story they might be, are still a barrier that the reader has to get beyond before the story-proper begins.
A prologue is a kind of pre-story, informing the reader of some event from the past that is necessary to understand the present...
If you believe that writing a prologue is necessary, write one (they are common enough in novels). Though it is a good idea to keep it as brief as possible. If you have some crucial backstory to get across but believe you can work it into the main body of the story - in the form of a flashback, say - do that instead.
Sometimes a prologue is literally entitled "Prologue". More often, it appears as a few pages of italicized text with no title (the fewer the number of pages, the better) before Chapter One begins.
Now for epilogues...
Here, you no longer face the problem of keeping the readers interested. If they have made it to the end of the novel, they aren't going to close the book at the start of the epilogue and demand a refund.
Epilogues, however, are extremely rare in novels, and that is probably all the reason you need not to include one.
Epilogues deal with the aftermath of a story. I don't mean the immediate aftermath, because all novels deal with that - either directly or by implication. I mean what happens to the characters 5, 10, 20 years after the novel's events have finished.
The question is, why would you want to show this?
What do I mean by "adds something"? Simply that your exploration of theme and character and so on should be enhanced by the addition of an epilogue, not dragged down by an unnecessary one - and the only way to tell that is, as always, to trust your instincts.
If you still aren't sure, forget all about writing an epilogue. They are so rare in contemporary literature that the reader is hardly going to miss one.
Nineteenth century novels sometimes ended with an epilogue, but they really aren't going to help you write a modern one.
If you wish to see what a contemporary epilogue looks like, try John Irving's The World According to Garp (it is the only modern novel I can think of with an epilogue).
You can make up your own mind whether the novel would have been just as good, or even better, without it.
Next Up: How to Find Titles for Novels...