Nothing went wrong. You are logged in as an ordinary user instead of root. As a general rule this is a GOOD thing. You should only use root when you absolutely must as it gives you G-d like privileges and lets you destroy anything and everything on your system.
To get back to root mode type in:
and it will ask you for your root password.
You are using BASH (Bourne Again Shell) whether you are root or an ordinary user unless you specifically choose another shell for your user account.
The reason you got a command not found error is because your path doesn't include /sbin as an ordinary user. If you want /sbin included in your path you need to edit your ~/.bashrc file and add it to your PATH= statement.