My nikon D40 takes doubles of every shot how do I turn this feature off?

What feature turns of the doubles of every shot on my Nikon
camera

I've had that happen with my Canon t1i - read your book right through. You should find it. Mine was a button I had pushed during a shoot.

You're probably shooting in burst mode or you had selected Raw+Jpeg for the quality.

If you're shooting both Raw+Jpeg, go in your menu "image quality" and chose the proper setting.
If you're shooting in burst mode, go to your menu "shooting mode" and chose "S" for single shot.

Probably Burst mode or RAW+JPEG mode. Easy fixes:
Burst: From the main screen press the magnifying glass with the + button and go down to the shooting mode option and select single (the top one)
-OR-
Menu-custom setting menu-shooting mode-single frame

RAW+JPEG: From the main screen press the magnifying glass with the + button, and go to image quality and select either RAW/fine/norm/basic instead of RAW+B
-OR-
Menu-shooting menu-image quality-(adjust from there)