The default password is the same as the default Raspbian password, that’s user name “pi” and password “raspberry”.
The additional setup is already documented here:
http://docs.emlid.com/Navio-APM/configuring-raspberry-pi/
There is no setup GUI so far as I know. You can install the desktop GUI but that is not recommended for drones (waste of resources) and won’t bring much as most of the configuration is done via APM/Ground Control software once you have the basic scripts and configuration files setup correctly.
Things to do are roughly:
- If you are using WiFi then configure that. You may have to read about WPA supplicant or other articles if you want to get WPA2 working. If you don’t intend to fly with WiFi (some people use that instead of FPV video, telemetry radio and some even instead of the RC receiver too).
- Download and install APM, but you probably want to follow the instructions to download the 3.3 release because the APM.DEB has not been updated and the 3.3 version is now produced directly by DIY Drones. It’s currently in “beta” phase. You can follow these instructions to get it:
APM 3.3-rc9 beta testing - #23 by CodeChief - Run APM (and usually add it to start-up too by editing “rc.local”). Connect to it’s IP address with your chosen GCS (e.g. APM Planner 2 or Mission Planner) and complete the configuration (skipping the “download firmware” part because the firmware download is replaces by the program you just downloaded in Linux.