The Fn key (also known as the Function key) is a feature found on most laptop computers. The Fn key allows keys on a laptop computer's keyboard to serve more than one function, a clever way of increasing the utility of the keyboard when space is limited. Dell laptops make good use of the Fn key, and if you own a Dell laptop, you should be aware of where the key is and how to use it.
Open your laptop and turn it on. Then locate the Fn key. It is located on the lower left side of the keyboard, next to the Ctrl key.
Press and release the Fn key. Now examine the keyboard carefully. You'll notice that many of the keys have icons or letters and numbers printed in blue upon them. These keys and functions are operated when the Fn key is enabled, as you've just done. Test it out by looking at the lower right side of the keyboard. You'll see two keys with small blue "sun" icons. These control the brightness of the screen. Press the lower one several times and you'll see the screen darken. Press the upper one. The screen brightens.
Press and release the Fn key again. Now try using the brightness keys. The screen brightness will not change. You've turned off the Fn key.