I guess you have an audio object placed on your layout and whenever you need to play a sound you call an event to play a sound file.
At these events, you need to add a condition to check your global variable if it is true or false.
On your setting page, you need to add an object with which your can interact.
You have a sprite of a square with is either checked or not (checked = playing sound; unchecked = sounds disabled).
When you click on that sprite, set your global variable either to true or false depending on what you need (like, if it is unchecked and you click on it, set the variable to true and change the sprite to show the checked image).
Hope this helps you to understand how variables are working and what you can do with events. If not, I would suggest to have a read of the C2 Manual first, as these functions are the basics for any game that you create with C2.