From EmbeddedSand

Once a serial connection is established with your Arduino, MegunoLink's serial monitor will display any serial data helping with debugging and allowing for data logging.

With no display, sending information out the serial port is the the most common way to debug Arduino programs. MegunoLink includes a tab to communicate with the Arduino over the serial port. Text received from the Arduino is written to a large text window. Send text to the Arduino using the combo box. Any message sent can be easily recalled from the combo box and these messages are saved with your project.

To start receiving data from the Arduino, select the COM port from the toolbar and press the connect button. Unlike the Arduino IDE, MegunoLink does not reset the Arduino when you connect, but you can trigger a reset at any time by pressing the reset button on the toolbar. Both buttons are available on MegunoLink's floating toolbar.

Programming the Arduino also uses the serial port. MegunoLink will automatically disconnect the serial port monitor when you start programming… and restore it when programming finishes.