What is a Treatment

You have an idea for a movie. A good idea. Maybe the best anyone's ever had. You've seen what's showing at the mall and, Lord knows, you can do better. You'll raise the money and produce your own film! Overwhelmed by your own ambition, you decide to just write it and ship it off to Spielberg. Yeah. He'll love it.
The storyline has been brewing for a long time now in your mind. The couple of friends bright enough to comprehend the significance of your idea have agreed that you've got a real winner. But they're gone now. They're home watching a game on TV, or cuddling it up with their special cozy while you, driven, misunderstood and lonely, sit and stare at your cold computer, willing something to happen after those magical first two words: FADE IN.

Agents, producers and movie studios receive hundreds of screenplays every year. Because of this, rarely does the buyer have the time to read each one without having some idea of what they are about to look at; hence the treatment becomes a very important selling tool. Atchity and Wong state that "second only to writing an entire screenplay or teleplay on 'spec', your treatment maybe the best tool for getting a foot in the door of moviemaking.
You need to write a "treatment". It's your first step and Step #1 is so simple you're going to feel embarrassed that you ever let it intimidate you. You wouldn't start assembling ingredients to cook a dish unless you knew what dish you're preparing; you wouldn't start out on a trip without knowing your destination. Don't start writing your screenplay until you know how your story ends!
TALK YOUR STORY OUT ON PAPER. That's all there is to it. Easy? Sure it is. You just start talking it out the way you'd talk it out with your best friend, letting it flow onto the word processing screen, or onto paper, or whatever. Don't worry about how it sounds or about the words you're choosing and, for heaven sakes, don't worry that it doesn't look like a script. That comes later. Right now, it more resembles a letter home. Once you get the entire story on paper, the beginning, the middle and the end, go back and edit. Spruce it up, tighten it, make it glow. Make sure it sounds a lot like what you'd say if you were telling someone about a wonderful movie you just saw. You wouldn't burden them with tedious he said-she said details. They'd fall asleep. And so will your reader. Just hit the glorious highlights, but in a logical sequence of events.

Go here for a sample treatment(they're not that easy to find online):
http://members.tripod.com/~e-luttrell0/scripttreatment-2.html

Another Treatment sample website (this one is my favorite because you can actually download the PDF!!):
http://www.scripthollywood.com/id28.html

Go here also:
http://www.filmmakers.com/features/screenwriting/treatment.htm

Hopefully this will be helpful to you!