How to use function keys without the fn key?

[Microsoft Windows]

I have purchased an external keyboard since the keyboard on my laptop has failed. I don't have the fn key on my external keyboard. So how can I use the function keys. I tried pressing them but no functions come. For example F2 is to lower the brightness but when I press F2 on external keyboard nothing happens. Also I have enabled the Action Keys in the BIOS menu of my HP laptop. So please help.

Continue reading...