From a Terminal window, enter:

su

This gives you superuser access using the user’s environment

eg. home is

/home/<user>

If you want to have superuser access as the Root user then enter:

su -

This uses the Root user’s environment eg. home is /root.

You can then enter the name (still in the Terminal session) of an app to run, such as Konqueror:

konqueror

and run it as Root.