Most of the time, Ubuntu will automatically have drivers available (via the Linux kernel) for your computer's hardware (sound card, wireless card, graphics card, etc.). However, Ubuntu doesn't include proprietary drivers in a default installation for a number of reasons. You can read more about Ubuntu's philosophical approach to free and non-free (think freedom, not cost) software and firmware in Mark Shuttleworth's blog. Mark Shuttleworth is Ubuntu's founder and currently its primary funder. New users tend to favor immediate functionality over long-term ideological gains, so if you have an proprietary graphics or wireless card, you may want to install the proprietary drivers for it.
