Apple - How to use F1-F12 keys with MacBook?

You have two options; either hold down fn as L2G suggested, or switch to the F1 etc. keys to work like that directly.

This can be setup in keyboard preferences here:

If you do that, F1 will work as the actual F1 key. If you want to use it for controlling the brightness, you'd hit fn with it.

To clarify and expand on HHH's comments: in at least some recent versions of OS X, F8, F9, F10, and F12 are set by default as shortcuts to control Expose, Spaces, and Dashboard. Houbysoft's and L2G's solutions don't work in this case; holding fn activates Expose/etc, and checking "Use all F1, F2, etc. keys as standard function keys" in System Preferences/Keyboard just means you get Expose from the unmodified function key instead of from fn + function key.

The solution is: in System Preferences/Keyboard, open the Keyboard Shortcuts tab, and find and uncheck the relevant shortcuts.

To expand on @Robert's solution (which in turn expands on @houbysoft's solution), to get F11 and F12 to execute application-specific functions (such as using F12 to open the developer tools in Chrome), you'll need to:

1. Execute @houbysoft's solution
2. Open System Preferences
3. Go to Keyboard
4. Go to Shortcuts
5. Click on Mission Control
6. Uncheck "Show Desktop" and "Show Dashboard"