How do you perform a function when there are no F keys on the keyboard?

I believe you have Touch Bar. This is relevant to macOS Ventura 13.4

The default setting to access F keys is to long press "fn" key on your keyboard. If it doesn't show the F keys in the Touch Bar, follow the steps below:

1. Open System Settings
2. Go to Keyboard
3. In keyboard navigation, open Touch Bar settings
4. Locate "Press and hold fn key to" and open the drop down option.
5. Select "Show F1, F2, etc. Keys" and then press "Done"

Now long press "fn" key to access the F keys.

Have a good day!