how to use the options with F10, F11, F11 for turning the sound up or down or mute?

Normally simply pressing them should do what you want, F10 to mute; F11 to decrease volume; F12 to increase volume. However, it's possible that you have a box ticked in Keyboard preferences which modifies the behaviour of the keys, requiring you to also hold down the Fn key (bottom left key on the keyboard) to enable the function.

Check System Preferences>Keyboard to makes sure the box indicated in the image isn't ticked.

One other feature which is not well documented - on later Mac System versions (it works on mine which is 10.7.5), if you hold down the shift and option keys on the keyboard and then press the F11 or F12 keys (to decrease or increase the volume respectively) the volume level will change in smaller steps. This is handy if you are trying to fine-tune the volume level and find that what you want is somewhere in between the normal settings.

You're welcome.

This was the perfect HELP. Thanks!