System Administration Guide, Volume I

Becoming Superuser (root)

Most administrative tasks such as adding users require that you log in as root (UID=0) first. The root account is also known as the superuser account because it's used to make system changes and can override user file protection in emergency situations.

The superuser account should only be used to perform administrative tasks to prevent indiscriminate changes to the system.

You can either log into the system as superuser or use the su(1M) command to change to the superuser account.

How to Become Superuser (root)

Become superuser by one of the following methods. Both methods require that you know the root password.