Communication between Android and Arduino

//Starts proximity sensor prog
long duration, inches, cm;
pinMode(pingPin, OUTPUT);
digitalWrite(pingPin, LOW);
delayMicroseconds(2);
digitalWrite(pingPin, HIGH);
delayMicroseconds(5);
digitalWrite(pingPin, LOW);

pinMode(pingPin, INPUT);
duration = pulseIn(pingPin, HIGH);
cm = microsecondsToCentimeters(duration);
lcd.setCursor(0,0);
lcd.print(cm);
lcd.print("cm");

//proximity sensor alert
pinMode(ledpin, OUTPUT);

if (cm < 20){
digitalWrite(ledpin, HIGH);
} else{
digitalWrite(ledpin,LOW);
}

//Bluetooth communication part

Serial.println();
Serial.print(temp);
Serial.print("C");
Serial.println();
Serial.print(cm);
Serial.print("cm");
}

//Part of config for proximity sensor
long microsecondsToCentimeters(long microseconds)
{

return microseconds / 29 / 2;
}

What is all that about?

...R