To use them, you'll need to press and hold the Fn key on your keyboard, which will make the F keys appear in the Touch Bar. From there, you can select the key for the desired function.

How to Disable the Fn Key on a Laptop. The Function key allows the user of a business laptop to access additional functions for dual-use keys.

Function keys that enable convenient features like instant browser refreshing or screenshotting pages are lost unless you hold down the “fn” key on your keyboard.

I'd like to be able to use my function keys without needing the "fn" key itself when I'm bootcamp-booted into Windows. Any ideas?