See this video: https://www.youtube.com/watch?v=gTmoyVFoGks
If you choose “set the password later” when you set up, you need to reset the password.
Go to instance detail, insert the new password for root, restart the instance, then you can login using SSH.
To prevent message: “sudo: unable to resolve host [abcdefg]” once run sudo, you need to edit hosts file
root@abcdefg:~# sudo nano /etc/hosts
add the hostname to that file, like this line bellow
complete file example:
#The following lines are desirable for IPv6 capable hosts
::1 localhost ip6-localhost ip6-loopback