The Fn key appears on notebook/netbook keyboards to provide a second meaning for an existing key. To get the second meaning, hold down Fn and press the other key. For example, it may be a key that turns the wireless radio on and off, changes the screen brightness, etc. Most desktop keyboards don't use a Fn key for this - if there are special purpose keys they are separate buttons.
Your first place to look for adjusting volume will be the operating system's volume control. You didn't say which OS you are using. The keyboard keys used for adjusting volume simply tell the OS to turn the volume up or down (usually), so there is no point in using the keyboard for this.
You say you have a Mini 10, but there are two distinct models by that name. Is yours the Inspiron 1010 or the Inspiron 1012?
Netbooks do not tend to have the numeric keypad overlay on the keyboard.