The function key is denoted by the symbol "Fn" on your keyboard. The function key works like a shift key to enable a second function on a dual-purpose key. The Function key is mostly used to control your laptop screen brightness and speaker volume. If turned on, the "Fn" key can produce unwanted characters while you are typing certain keys on your laptop keypad.
Locate the "Number Lock" key on your keypad; it is often abbreviated as "Num Lk." Some manufacturers like Sony Vaio combine "Num Lk" with "Scr Lk" (Scroll Lock). This key is typically located at the top right-hand side of your keypad.
Press the "Num Lk" key once. This will turn off your function keys.
Press "Num Lk" key again to turn on your function keys.