Assuming you would like to return to the Ubuntu Desktop from the Terminal, there are a few commands that can help.
First, you can use the exit command to close the current shell. This will take you back to the previous shell or terminal.
If you want to log out of your account and return to the login screen, you can use either the logout or reboot command.
Finally, if you want to shutdown your computer, the command is simply shutdown. You can also add an option for when to shut down by adding -h now for an immediate shutdown or -h XX:XX for a specific time.