Starting up Armbian version of Ubuntu Desktop on your Banana Pi (BP) for the first time....

Once you connect your BP via ethernet to your network, your BP will be issued with an IP address by the DHCP server of your router. You may need to look inside the router to find this IP address; look at "connected devices" (or similar).

Once you know the IP address, and using PuTTY (a free SSH client - download from here), enter this IP address into Host Name box and log into the BP.
The basic, pre-set, root username/password is root/1234
You will immediately be asked to change the root password so enter a new root password (twice).
You will then be asked for a user name and for a user password. Enter these, these being the normal ones you will be using to login to the Pi
You will also be asked for some additional info like group name, room number, phone number etc. None of this is mandatory so it's OK to press enter for each one. 

 Now you have your own username and password it is strongly advised to disable root login.

To do this (whilst logged in as root) ....

 $ nano /etc/ssh/sshd_config

Find this section in the file, containing the line with “PermitRootLogin” in it....

change PermitRootLogin yes to PermitRootLogin no

 $ sudo reboot 

 Update and upgrade
$ sudo apt-get update
$ sude reboot
$ sudo apt-get upgrade

Next, config your install...

$ armbian-config

Work your way through the menu item BUT I can never get the Network section to work; I always wish to set a static IP address and I find the below to be far better...

$ sudo nano /etc/network/interfaces

Change the following...

 add # to beginning of line:
 iface eth0 inet dhcp
to read
 #iface eth0 inet dhcp  
add lines:
 iface eth0 inet static

$ sudo reboot


and work through each category.

Your Banana Pi is now setup with Ubuntu Desktop.