On/off is controlled by the switch on the box. With any USB keybaord/mouse the lack of power to the USB port when the device is off makes on/off impossible.
The @ symbol is FN + " (the bottom right key). The @ and " symbols are reversed, which I think is a problem with US vs UK keyboard settings. I haven't managed to figure out how to change it but it's almost certainly possible.
Which button is mouse on/off?
Tomorrow morning I'll post a graphic here showing exactly how the F10 is mapped in Windows 8.1. It will be a useful reference.