This article explains how to turn on the keyboard backlight on an HP laptop. It may vary slightly for some, especially older models, but most HP laptops use the same method and have the key in the same place.
How to Use the Keyboard Illumination for HP Notebooks | HP Support
HP has made the process of turning on the keyboard backlight extremely simple. Most modern HP laptops require just one press of a button to turn the keyboard backlight on and off.
If your HP laptop is not already on, turn it on now by pressing the power button.
Find the light button on your keyboard. It’s located in the row of Function F-keys at the top of the keyboard and looks like three squares with three lines flashing from the left square.