BIOS is the low level program that comes with your computer's motherboard to get it to the point where the operating system of choice can do something with it (we're talking really basic stuff like recognizing memory, the power on self test, responding to keyboard input, booting from some drive, etc.). There are usually various settings associated with tis process. Usually these settings are stored on some sort of non-volatile (meaning it doesn't go away when you take power away) memory (actually, that isn't even true, as the way it often works is that there's some memory which is powered by a battery --so that power never really goes away for the BIOS setting information). In the case of some older Compaqs (I don't know if Compaq still does this), they actually used a special partition on the hard drive to hold some of this information (as well as for some low level diagnostics).
Generally, the BIOS settings will be available by hitting some key or key combination at boot time (there usually is a message at boot time indicating how to access these settings such as, for example, "Press the <DEL> key to enter setup" --but this message can be disabled on many computers). Your computer manufacturer should have the information on how to access the BIOS. The most common way nowadays is probably to hit the <Del> key during the beginning of the boot process (often very shortly after turning it on --it can be easy sometimes to hit it too late in the boot process). Other key combinations are also possible, for instance, <F10>, <F2>, <Ctrl>-<Alt>-<Enter>, hitting Reset twice, <Ctrl>-<Alt>-<?>, <Ins>, <Esc>, <F1>, <Ctrl>-<Alt>-<Esc>, <Ctrl>-<Alt>-<S>, <Ctrl>-<Alt>-<Ins> (from
http://www.computing.net/faq/content9x/bios.html).