OK, first you need root your phone, next you must put this widget to your home screen.
You can check this video for what's widget and how to add them:
http://www.youtube.com/watch?v=kW9DWjDTpUkThen you can just click the widget and use it. For advanced usage there is advanced settings, which can set the freqs automatically. Don't forget to save changes.
If you want to extend battery power, you can just lower the freqs, but be carefully don't make it too low. Also, you can make it lower when screen off and higher when screen on in advanced settings.
Hope it helps and you like this widget.