Noob power problem in connecting a LDR

Well, I'm working on a project, an arduino powered night light..Just for my first try with arduino.
I've seen lots of tutorials using the LDR..But I've found them connecting a pin to 5V..But i'm using a 9V power source..So will i connect that pin to 9V or to 5V and please, i wanna know why.
Also, I've found some people using 10 Kohm resistor and others using 22 Kohm resistor..So which one is better to use?
Here is the LDR that i will use..

And thanks

If you are using an Arduino to monitor the LDR use 5v. Use what is already there.
What are the dark and light on resistances?

Well, i didn't understand the second question.
And..Umm, what you mean with monitoring the LDR? I will use the LDR to turn on and off the LED.

Are you going to use the Arduino connected to the LDR, then use the Arduino to turn on a light?

Yes, a night light.

The LDR would be connected to a series resistor. The junction of the LDR and the resistor goes to an analog input.
+5---- LDR------resistor-----GND
|______analog input

The dark resistance can be measured with a DVM with no light falling on the LDR.
The light resistance is the measured value of the LDR with light on it.

The value of the resistor depends on the values read from the LDR mentioned above.

You could try a 10k resistor with the LDR.

Then use serial print to see what the input voltage range is, then write your "if" code accordingly.