Arduino serial communication is one of the many ways Arduino talks to other devices. Arduino uses asynchronous serial communication to send-receive data to and from other devices. Arduino Uno supports serial communication via on-board UART port and Tx/Rx pins. Generally this transmission happens at 9600 bits per second which is termed as baud rate.

Arduino may communicate with many devices including:
- Another Arduino
- A computer
- LCD display
- Modem
- Or any device that supports serial communication
How to do it?
In this example we’ll connect Arduino and a computer using UART port. For this we are going to use Arduino IDE’s Serial Monitor. Serial Monitor will display data we sent from Arduino Uno.
Code:
void setup() {
Serial.begin(9600);
}
void loop() {
Serial.println("Hello World...");
delay(1000);
}
Upload this code and select Tools > Serial Monitor (Shift+Ctrl+M). You should see this output.

Further Reading: