root is the name of the administrator user on the system. The "root prompt" is what is printed by a command-line "shell", and you can enter into it textual commands.
I don't know what this "escape" is you mentioned, please could you describe what you mean?
If you are looking at a screen with "root@d-desktop:~#" on it on the computer which you are talking about (where you want to find out what username and password you set up during installation), here's how:
To find the user name which was set up during installation of Ubuntu, type in this command (this is case-sensitive):
grep x:1000 /etc/passwd | cut -d: -f1
In my case this prints out my user name, "matthew"
There is not a good way to get the original password for this user, but you can reset it to a new value with this command:
Of course, you will have to replace the "matthew" in that command with whatever your user name is. You will be prompted to enter the new password twice to protect against typing errors.