Reference → Serial →

println()

Prints data to the serial port as human-readable ASCII text followed by a carriage return character (ASCII 13, or '\r') and a newline character (ASCII 10, or '\n'). This command takes the same forms as Serial.print(). Serial.println(val)
Serial.println(val, format) val the value to print - any data type format pecifies the number base (for integral data types) or number of decimal places (for floating point types) size_t (long): println() returns the number of bytes written, though reading that number is optional 
        int analogValue = 0;    // variable to hold the analog value

void setup() {
  // open the serial port at 115200 bps:
  Serial.begin();
}

void loop() {
  // read the analog input on pin 0:
  analogValue = analogRead(0);

  // print it out in many formats:
  Serial.println(analogValue);       // print as an ASCII-encoded decimal
  Serial.println(analogValue, DEC);  // print as an ASCII-encoded decimal
  Serial.println(analogValue, HEX);  // print as an ASCII-encoded hexadecimal
  Serial.println(analogValue, OCT);  // print as an ASCII-encoded octal
  Serial.println(analogValue, BIN);  // print as an ASCII-encoded binary

  // delay 10 milliseconds before the next reading:
  delay(10);
}