[seharper]

All the grounds coming from all the cables coming into the box MUST go together. They are not spares; you don't use one of them. They must connect to each other. They must also go ONE of the following:

- (if the box is metal) to the metal box. From the metal box, ground will be carried to the switch via its mounting screws and its metal yoke. You don't need an additional ground wire; that will suffice. Do Not disconnect the ground off the metal box and put it to the switch instead; common newbie error and code violation.
OR
- (if the box is plastic) to the switch. Use the pigtail coming out of the top of the green nut for that. If you're connecting two switches, feel free to pigtail 2 wires off that using a regular wire nut.

If the yoke is not metal, check it for a safety listing from UL, CSA or ETL. None of those? Only "CE" (a garbage mark on a USA-marketed device)? Back to Amazon it goes. (or really back to the 3rd party seller via Amazon).