Complex sentence: If it is you will need to press the "Function" or "Fn" key at the same time; this is normally in the very bottom left and will often be marked in a different colour to the letter keys.
Split into simpler sentences: If it is a different colour, you will need to press the "Function" or "Fn" key at the same time. That key is normally in the very bottom left and will often be marked in a different colour than the letter keys.