From my last post (Arduino-oled-display) I added a new function that allows me to send notification/messages from my terminal (linux) to my Arduino and it shows it through the little Oled screen. Here I will share the commands and code lines to get done the serial communication on your project.

void loop() {
  while (Serial.available() > 0)
    {
        char recieved = Serial.read();
        inData += recieved;

        // Process message when new line character is received

        if (recieved == '\n')
        {
            Serial.print("Arduino Received: ");
            Serial.print(inData);
            //digitalWrite(ledPin, HIGH);
            //
            if(inData == "HELLO\n")

            { // DON'T forget to add "\n" at the end of the string.

              Serial.println("HELLO");
              //digitalWrite(ledPin, LOW);
              display.clearDisplay();
              display.setCursor(0,0);
              display.setTextSize(2);
              display.print("Hi jose!");
              display.display();
              delay(3000);
            }
            inData = ""; // Clear received buffer
        }
    }
}