A prologue is on the first page or before the story starts. It is where you can establishing something that happens before the current and real story starts. It is also used by authors to give the reader a little glimpse of what to expect once the real story starts. It is like a build-up of events before the story starts. It is included always in the front matter and gives the reader some extra information about the opening of the story.
It originates from the Greek word Prologs which means before the start basically it tells another story that leads up to the main story. It can have dialogues and characters or could be told with another voice than the one telling the story. Ideally one should keep them short and crisp.
An epilogue is at the end of the story and tells the journey or story of the characters after the real story ends. It severs more like a conclusion and always comes sat the end of the book. It is used to reveal the fate of the characters and can also be used to hint at the next sequel of the book. They are used both in books and films.