The use of a ring or wearable with Fidesmo Car Key is exactly the same than a standard Tesla Card.
To activate your Fidesmo Car Key on your Tesla, please read this article.
Locking and unlocking the car
To unlock the car simply approach the ring (or wearable) to the NFC reader placed in the B-pillar below the lateral camera.
If the car does not unlock immediately, it might have entered in a power saving mode. Then a quick tug on the door handle can wake it up, at which point the wearable will be easily read again.
You should use the same gesture to lock the car.
Starting the car
Simply approach the ring (or wearable) to the NFC reader placed behind the cup holder