User Manual

Lesson 4 Open Arduino Serial Monitor
The Arduino IDE has a feature that can be a great help in debugging sketches
or controlling Arduino from your computer's keyboard.The Serial Monitor is a
separate pop-up window that acts as a separate terminal that communicates
by receiving and sending Serial Data.
Connect the Arduino UNO R3 motherboard to the computer via USB,selecting
a port for uploading Arduino code. Go to Tools > Port, and select the correct
port.
Then simply click the Serial Monitor icon:
you can see the Serial Monitor like this: