Error Message

Hi, I am having trouble understanding what an error message means. I'm hoping someone can let me know what I need to do and what I am doing wrong.

This is the error message I get when I try and run the code,
*****Arduino: 1.8.3 (Windows 7), Board: "Arduino/Genuino Uno"

C:\Users\User\Documents\Arduino\sketch_NeoPixel_Colored_Light\sketch_NeoPixel_Colored_Light.ino:1:31: fatal error: Adafruit_NeoPixel.h: No such file or directory

#include <Adafruit_NeoPixel.h>

^

compilation terminated.

exit status 1
Error compiling for board Arduino/Genuino Uno.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.****

I am wondering what this means and what i need to do to solve this.
Here is the code I have written,

#include <Adafruit_NeoPixel.h>
#include <KosmoBits_Pixel.h>

KosmoBits_Pixel pixel;
int red= 0;
int green = 0;
int blue = 0;
int brightness = 0;

void setup() {
// put your setup code here, to run once:

}

void loop() {
// put your main code here, to run repeatedly:
brightness = 50;

// red
red = 225;
green = 0;
blue = 0;
pixel.setColor(red, green, blue, brightness);
delay(500);

//green
red = 0;
green = 225;
blue = 0;
pixel.setColor(red, green, blue, brightness);
delay(500);

// blue
red = 0;
green = 0;
blue = 225;
pixel.setColor(red, green, blue, brightness);
delay(500);

// purple
red = 225;
green = 0;
blue = 225;
pixel.setColor(red, green, blue, brightness);
delay(500);

// turquoise
red = 0;
green = 225;
blue = 225;
pixel.setColor(red, green, blue, brightness);
delay(500);

// yellow
red = 225;
green = 225;
blue = 0;
pixel.setColor(red, green, blue, brightness);
delay(500);

// white
red = 225;
green = 225;
blue = 225;
pixel.setColor(red, green, blue, brightness);
delay(500);

}

Where did you install the libray?

.