How do I install the drivers for my graphics card, which is an ATI 6850? I know that sometimes things stop working when I download a third-party driver, so I'd like to know the right way to do this.
By default Ubuntu will use the open source drivers for AMD cards. Some users prefer the third-party AMD/ATI drivers for various reasons and it's easy to install them. The easiest way to install these drivers is to either search for the "fglrx" package in the Ubuntu Software Center and install it (and then restart) or open the "Additional Drivers" application and choose to activate the AMD driver when asked (and then restart).
If you prefer to input commands in the terminal: