The root user on the base SDF image has the default password "root" and should be changed to something more secure before you enable networking! While logged in as root, type
passwd and follow the prompts to set the new password.
It is a good practice to create a regular user account for day to day use.
useradd -m <username>
Add this user to the "sudo" group so that it can run commands as root.
usermod -aG sudo <username>
In your control panel at vps.sdf.org, note YOUR_IP (e.g. 188.8.131.52) on the top line, and YOUR_HOSTNAME (e.g. ubuntu99).