Using function keys in-game?

[milshake]

I was recently playing Left 4 Dead 2 when my teammates began voting on whether or not one of our teammates should be dropped. The instructions for voting said to press one of the function keys, like f5 or some other function key, except macbooks have default functions bound to those keys, like decrease screen brightness, volume, etc. Is there a certain combination of keys to press with a function key to make it work?

[Princess Penally]

If you play games like L4D2 or CS:GO, you will quickly learn that a lot of people will dislike you for not voting on something. The way all Mac users have to fix this is the following: Open System Preferences >> Keyboard >> Keyboard >> "Use all F1, F2 etc. keys as standard function keys".
After using this, there is a downside, you may be able to vote on a game, but you then have no way to quickly minimize the game, edit the volume or brightness. When I usually play the two aforementioned games, I have maximum brightness and a volume of 2 or 3 bars with 100% volume in games (with in-built speakers, not microphones or headphones).
Hoped this helps!

[Princess Penally]

Also when this is enabled, using F5 still gives screenshots and using F11 shows the desktop (kinda).

[milshake]

Thank you, this helps a lot!