Go to your System Preferences, then the Accounts pane (might be "Users & Accounts", or "User & Groups" on yours)
You should see a list of user accounts
One should be the one that you are logged in to: System Admin, or may say "root" (which is the root user account, and not one that is normally used except for special purposes). The root account leaves your Mac vulnerable to outside access.
What OTHER accounts are listed in that pane?
If no other accounts, then add one for yourself.
Once you have that added, you should be able to log out (probably after a restart, when you should now see a login window where you can choose the account that you just created, and you should be able to log in to that new account. The account "Other" will only be accessible then if you know the password for that account.
Let us know how that goes.
You should see a list of user accounts
One should be the one that you are logged in to: System Admin, or may say "root" (which is the root user account, and not one that is normally used except for special purposes). The root account leaves your Mac vulnerable to outside access.
What OTHER accounts are listed in that pane?
If no other accounts, then add one for yourself.
Once you have that added, you should be able to log out (probably after a restart, when you should now see a login window where you can choose the account that you just created, and you should be able to log in to that new account. The account "Other" will only be accessible then if you know the password for that account.
Let us know how that goes.