sudo command (you must do this every time you issue a command)
sudo -i command (this gives you persistent access)
If you are launching a graphical app like Nautilus (file manager) use gksudo instead of sudo. This makes it so that your files created in Nautilus, Konqueror, or Dolphin are owned by your user and not root.
If you are using KDE instead of gnome, use kdesudo instead of sudo to launch graphical applicaitons. Example:
kdesudo kate ~/myfile.txt
Create an Ubuntu root account with password easily.
This post also shows how to create a linux cd root password.