The serial gadget is the simplest gadget on the USB Ninja platform. By default, a TTY is made available over the connection and is the quickest way to get started. The default login is alarm:alarm and the root account is root:root.
On Linux and MacOS, you can connect to the TTY with either screen, minicom or some other program. Personally, I prefer minicom.
screen /dev/ttyACM0 115200minicom -b 115200 -D /dev/ttyACM0
NOTE: You'll probably need root to be able to open the /dev/ttyACM0 file.
On Windows, you can use PuTTY to connect. Just make sure the baud-rate is set to 115200 and you should be good to go!
Once you're connected, you can set up WiFi for easier SSH access or whatever you want! The image contains a full Arch Linux install, so you can treat it like any other system.