USB serial console
The openSPOT4 shows up as a USB serial port (COM port) when plugged into a computer. You can reach the serial console by opening this USB serial port with serial terminal software like PuTTY, RealTerm, TeraTerm, minicom etc.
To find out which is your openSPOT4's serial port device path (COM port number), look at the device list of your computer (in your operating system's control panel for example). You can use the following settings for opening the serial port, but in theory any configuration would work: baud rate 115200, 8 data bits, no parity bits, 1 stop bit.
The openSPOT4's serial console does not require drivers on modern operating systems, as it shows up as a standard USB ACM device.
The serial console can be used to change network settings, reboot the openSPOT4, switch it to bootloader mode, see its debug log, reset the web interface password and many more. The list of available commands can be queried with the help command.
You can turn on the device log over the USB serial console by entering the log command.