For ESL, your English is excellent!!
Depending on your distribution, you should be able to log out, and then log in as "root" using the password that you provided during install. If you did not supply one, then it should let you in with no password.
Before doing anything else, assign a password by typing passwd in a terminal.
In some distros, eg Ubuntu, the root user is disabled. Activate it using sudo passwd root.
Once you know that root is activated, you type "su" in a terminal become root.