More often that not, a keyboard will have extra functionality keys that you can bind to different operations. Xbindkeys makes it easier to make each key perform a specific task.
First, run “xbindkeys -k” to determine the code for a key. For example:
"Scheme Command" m:0x0 + c:160 NoSymbol
Then change the “Scheme Command” section to the command that you want to run when the key is pressed. For example:
"amixer set Master 5%+" m:0x0 + c:176 NoSymbol
Place your newly created command in ~/.xbindkeysrc and add xbindkeys to your ~/.xinitrc.