For security reasons, administrative tasks in Ubuntu can only be performed by users with special administrative privileges.

Administrative access can be given to individual users, who can use the sudo command to perform administrative tasks. The first user account you created on your system during installation will, by default, be able to perform administrative tasks.

When you run an application that requires administrative privileges, you will be asked to enter your user password. This ensures that rogue applications cannot damage your system, and serves as a reminder that you are about to perform administrative actions which require you to be careful!

All of the default graphical configuration tools in Ubuntu already use sudo, so they will prompt you for your password if needed.

Each time you type your password, the system remembers it for 15 minutes so that you do not have to type it again.

For more information on the sudo program and the absence of a root user in Ubuntu, read the sudo page on the Ubuntu wiki.