In my project, I need to press the volume buttons and get it to actually to change the volume and not just hit F12 or F11, so I need to be able to press the 'funtion' key. I looked through and there's no key for 'function' in the library. Is there any way I can add the 'function' key to my program?
Do you really have a "function" key on your USB keyboard?
I have such a function key on my internal notebook keyboard. But usually the function key is not sent as a key or modifier but the keyboard internally activates other keycodes for the different key that have double meanings.
As far as I know the scancodes for these special keys are not standardized but most keyboards today use
e0 30 for volume up
e0 2e for volume down
Hope that helps.
The Keyboard library is currently only sending reports for USB/HID Page 0x07: the Keyboard/Keypad Page. It sounds like you want to send the volume control keys from USB/HID Page 0x0C: the Consumer Page. That will require changing the Keyboard library or making a separate library to allow sending codes from Page 0x0C. The codes you want are 0xE9 (Volume Increment) and 0xEA (Volume Decrement)
See the HID Usage Tables document:
http://www.usb.org/developers/hidpage/Hut1_12v2.pdf