Unless you are using AWS or another shady cloud provider that alters the root/sudo users, so the default user should be root
that you use to setup a new cloud server with SlickStack the first time… during install you choose the username of your sudo user or just keep the default sudo username that the script will generate for you.
After that, reboot and going forward you login SSH on Port 22 with that sudo user… every time you login it should automatically drop you into the /var/www directory where you should see the bash scripts from SlickStack.