I presume you're using a portable (MacBook or MacBook Pro). To get the function keys to be seen by a program rather than interpreted by the Mac, hold down the "fn" key (lower left of the keyboard) and then press the function key. (I.e., hold down "fn", then press "F5".)
You can also go into the Keyboard & Mouse preferences and reverse the meaning of "fn". (I.e., F5 will be seen by the program and fn+F5 will control the volume.)