Let's make the circuit  -

 Connections 

 Light-emitting diode [ LED ]

 Negative of led to Resistor 

 Resistor to Gnd of Arduino

 Positive of led to pin no 13 of Arduino

Note -  Actually I am using the LDR sensor module but I will show connections for both. 

Connections 

 Light sensor module 

A0 pin to A0 pin, Gnd to resistor 

Resistor to Gnd of Arduino 

VCC to 3.3v

No connections for pin D0

Note: These connections are if you have a single LDR sensor like shown here : 

Connect one end of this sensor to one leg of the resistor 

And another resistor to Gnd 

Connect another leg of this sensor to Pin A0

Code

Here is the code : 

const int ledPin = 13;
const int ldrPin = A0;
  void setup() {
  Serial.begin(9600);  
  pinMode(ledPin, OUTPUT);
  pinMode(ldrPin, INPUT);
}
void loop() {  
    int ldrStatus = analogRead(ldrPin);
    if (ldrStatus <= 800)
 {
   digitalWrite(ledPin, HIGH);   
  Serial.print("Its Dark, Turn on the LED:");  
  Serial.println(ldrStatus);  
}  
else  {
   digitalWrite(ledPin, LOW);   
  Serial.print("Its Bright, Turn off the LED:");  
  Serial.println(ldrStatus);
  }
}

When there is sufficient light the led will remain off.

And when there is darkness the led will remain on. 

The threshold given in the code is 800.

Finally, the project is completed !!!