What does the FN key actually do?

Solution 1:

It's a hold functionality:

On keyboards with an Fn key, hold down Fn and press the key to use the alternate commands.

There are two possible explanations for what you're experiencing:

• You're releasing FN before pressing F3.
  • Plausible during speed runs.
• You're locking the FN key accidentally.

There is some official documentation on the latter case for windows-10 computers:

If your keyboard has an F Lock key, press it to toggle between the standard commands and alternate commands.

• When the F Lock light is Off, alternate functions work (Help, Undo, and so on).
• When the F Lock light is On, standard functions work (F1, F2, and so on).

If you have an all-in-one keyboard, the F lock works slightly different:

To enable FN Lock on the All in One Media Keyboard, press the FN key, and the Caps Lock key at the same time. To disable FN Lock, press the FN key, and the Caps Lock key at the same time again.

Solution 2:

A laptop's Fn key (Function Key) is to give the buttons extra functions using the same keys. There are many different flavors for this, so unfortunately neither the placement nor icons are standardized.

In this screen shot, you will see a padlock with Fn inside, and that's a typical "Function Lock", locking the buttons to work as the F1-F12 keys, or the media keys:

Here you see the keys with the Media functions as the large icon, and the F1-F12 keys as the alternate options. Function Lock is still via the ESC key though:

The On Screen Keyboard on Windows 10 may have the Function Lock on the SHIFT key:

Some keyboards even have a dedicated button just for "Function Lock"