Exposition. Explanation. You use it to describe necessary story elements that you either can't or don't want to handle with dialogue between two story characters.

A few quick guidelines:

Big "chunks" of exposition are boring to read. If you've got a long, complicated backstory (i.e., the stuff that sets up the story you want to tell), you have a number of choices.

(1) Put in a "foreword" or "preamble" -- a few paragraphs of information explaining to the reader whatever it was that caused Captain Picard to leave Star Fleet and settle down to take up a new career as a librarian in a small town somewhere in the Alpha Quadrant. It's easy. It's quick. It's fairly boring, of course. A lot of readers won't care, some of them won't read it, most of them will skim it quickly and forget it. Personally, I'd suggest leaving this as a technique for filling the reader in on crucial events in previous stories when you're in the middle of some long, complicated series.

(2) You can have your character go sit on a beach, or in a bar, or go for a long drive. Have them review the events of the past year or whatever of their life or however long you need. Unless this is a really brief interlude, you're back into boring territory here.

A long passage of exposition sets up a placid, nothing-much-happening-here attitude in your story. When you make the transition from "remember then" to "act now" -- the reader is going to have to shift moods abruptly. And anything like an abrupt shift in a story throws the reader out of the universe you're trying to create for them. It will take them a while to sink back into your world.

(3) The flashback. Beloved of authors everywhere. And almost never handled correctly. This is as bad as the "remembering on the beach" idea. In fact, most of you probably thought I meant a flashback in the above example, didn't you?

(If you're interesting in reading an entire digression on how to write that flashback that you have your little heart set on, go to "No U-Turns" and get a few pointers on how it's done.)

(4) Blend and Weave. You need exposition. It's critical to the story-telling process. It fills the reader in on non-verbal cues, actions, and physical locations. Exposition gives a story depth and texture. So do include it. But put it where it belongs. It's part of the story. A little bit here. A little more there. Another few lines half a page down. Blend in the explanation of how the characters got where they are with bits of dialogue, short thoughts, and quick clues to physical surroundings. And keep it alive. Here's an excerpt for you, written with a lot of the same mistakes we all see ourselves making sometimes:

Ray lay in the hospital bed, sulking. He still couldn't believe that Fraser had beaten him up. He had black eyes, cracked ribs, a swollen jaw, and enough bruises to wallpaper Wrigley Field. And, why?

'Verisimilitude, Ray,' Fraser had told him. Fraser said that that if they were going to pretend to be drunks in a barroom brawl, they'd better make it look good. He hadn't said it like that, of course. He'd used a lot of fancy words and tried to make it all sound logical.

Ray wasn't fooled, though. Behind some of those punches, he'd felt real anger. This loss of control by a guy who was so anal and locked up that his hair never even got messed up, was scary.

Not bad, huh? I mean, you've told the reader that the guys were undercover. You gave physical locations (a bar for the fight, the hospital room now). You said Fraser's mad, and letting the reader assume it's at Ray, but the reader can't be sure of that. You know that Ray's worried.

You may be feeling a bit smug about this as an opening for your story. I mean, heck, you worked in your entire backstory in a few short lines! Cool!

Of course, it's clumsy and kind of boring. A lot of readers are barely going to skim it because they're trying to get past the filler to get to the "good parts." The good parts are where something actually happens on-screen (or, on the page). Maybe the guys are on-screen at the same time. Maybe Ray's trying to bully the doctor into releasing him immediately. Whatever--as long as something is happening. Never mind that you're in love with this passage, which you think is full of subtle clues about what's going to take place later in the story--a lot of your readers aren't going to be paying that much attention.

And, that's bad. You want your readers paying attention from the first sentence, from the first word of your story. The easiest way to give the illusion of something happening while you're filling in the backstory, is to let something happen. Put two people on-screen at the same time.

There are a lot of ways to re-write the bit above to allow this. Ray can be lying there in the hospital bed as the doctor makes an examination, mentally cataloging how he got every cut, every broken bone, every bruise.

Only one eye was swollen entirely shut, so Ray could peer out of the other one to watch the doctor reading his chart.

"Let's take a look, shall we?"

She had that irritating bedside manner, that way of talking to a patient like they were a helpless child that always pissed Ray off. You look, lady. You're the one with two good eyes, right?

She tipped his chin with a cool, professional touch and shone the inevitable small light into the partially open eye.

That's right. Start there. That was the first one. The physical shock of that first, painful blow shuddered through him again.

"Does the light hurt?" She'd misinterpreted his response. A barely perceptible shake of his head reassured her. "These eyes don't look too bad."

You should try them from the inside. He almost thought he'd said it out loud, but she didn't react.

"How are the ribs?"

They're ready for basting and roasting. How the hell did she think they were? They were broken, that's how they were. His partner, his best friend had fucking broken two of his ribs in a barroom brawl that was supposed to be a staged fight to solidify their undercover assignment.

Look at the jaw, doc. What about the jaw? That had come last, a roundhouse punch out of right field that had lifted Ray off his feet and landed him in this miserable, antiseptic-infested hospital bed.

"Is there any sign of internal bleeding from the contusions on the abdomen?" This time her question was directed at the nurse, standing by with Ray's chart held efficiently in front of her.

Internal bleeding? Check the chest area. I think you'll find some damage there. But those bruises wouldn't show. He'd trusted Fraser. They'd discussed the fight. Even sort of choreographed it. All at Fraser's insistence.

'We need to insure our encounter offers verisimilitude, Ray.' And Ray fallen for it. Like a fool, he stood there and let Fraser throw that first, wicked punch. And then, with his head still reeling, he'd been forced to absorb other, harder blows. Punches with real anger behind them.

And that was worse than anything else. Because that kind of loss of control by a guy like Fraser who was wound so tight that his hair never even got messed up, was kinda' scary. In fact, it was frightening.

Hopefully you see that version as an improvement. Because, instead of two or three short paragraphs of Ray remembering what happened, you have him reliving parts of it. His pain, his sense of betrayal, and his worry about Fraser are clearly shown to the readers. Notice how I've worked some of the exposition into Ray's internal dialogue. Some is still his indirect thoughts, but that's all right. You can't avoid that kind of thing entirely and you don't want to try. You just don't want to overdo it.

In addition, the use of dialogue, even internal dialogue, means that the character's personality is allowed to shine through. The first example above could have been either one of the Rays, there's no way to know. This second one is more clearly Kowalski. (It would have been better, but I'm not a Due South expert, sorry.)

Another option would be to have Ray on-screen with Fraser in the hospital room. Fraser is trying to explain what happened and Ray is refusing to answer. Instead, he carries one a similar internal dialogue, thinking bitter remarks and wondering what the hell got into his partner.

Or the guys can actually talk to each other. Fraser naturally comes to visit his partner in the hospital. The surface conversation can get deeply into what happened unless you have a reason to save it for later in the story (for instance, if the reason Fraser is angry is too important to your story to be revealed now). If that's the case, just make their conversation awkward, just touching the surface of what happened and, again, Ray's thoughts fill us in on how he's feeling and his reaction to Fraser's apparent betrayal of their friendship.

Exposition is a necessity, but don't drown the reader in it. And don't throw it all into the story at once. Lead the reader on. Give them bits of explanation now and again, whatever you can without revealing too much of the story in advance. Entice them to read on to figure out why Fraser is that angry with Ray and what happened either between them, or to Fraser, to cause this completely uncharacteristic outburst.