Writing Prologues and Prefaces

A prologue (or preface) is a small chapter in the beginning of the book.
Yet there is a lot of confusion about how these things actually work.

To start, prologues depict events that have happened before the action in Chapter One. Usually they depict the character's childhood or an important event that happened years ago (such as the beginning of a war.)

I've noticed a lot of books where the prologue isn't used like this. Some writers think that a prologue is just an awesome scene used to pull the reader in.
Sure, it can be awesome, but if it would work as Chapter One, make it chapter one.

The prologue isn't the place where you introduce the main character or the main problem.

For example; if the prologue contains a scene where a character gets captured, then Chapter One shouldn't detail him waking up in his prison. The capture scene is Chapter One and should be labeled as such.