If you're using MacBook keyboard, you will see a Fn key. When this key is pressed, F1-F7 keys will become standard function keys.
Fortunately, you can change this behavior so that without pressing down Fn key, F1-F7 keys are already functioning as standard function keys.
The good thing here is, you can easily perform keystrokes that include these keys, such as Control F1.
Here are the steps to change these function keys' behavior: