Serial Event

This example demonstrates use of the SerialEvent() function. This function is called inside the loop(). If there is serial data in the buffer each character found is added to a string until a newline is found. In this case the string made by the characters received so far is printed and set back to null.

Step 1: What You Need?

1 x Arduino Board ( Arduino UNO R3 used in this tutorial.)
1 x USB Type B cable

Optional 

Arduino Uno R3 Acrylic Transparent Casing

Arduino Compatible UNO Ultimate Starter Kit / Learning Kit

Don't have components? Don't worry. Just click the component's name. 

Step 2: Build Your Circuit.

None, but the board has to be connected to the computer; the Arduino Software (IDE) serial monitor may be used to communicate the single or multiple characters and receive the string back.

Step 3: Upload The Code.

1. Select the Arduino board type: Select Tools >> Board >> Select your correct Arduino board used.

2. Find the port number by accessing device manager on Windows. See the section Port (COM&LPT) and look for an open port named "Arduino Uno (COMxx)". If you are using a different board, you will find a name accordingly. What matters is the xx in COMxx part. In my case, it's COM3. So my port number is 3.

Select the right port: Tools >> Port >> Select the port number.

3. You can find this code in the example of Arduino IDE.

Select File >> Examples >> 04.Communication >> SerialEvent

Click press the "upload" button (see the button with right arrow mark).

Download: 

Arduino IDE

Sources:https://www.arduino.cc/en/Tutorial/SerialEvent

04.Communication library SerialEvent