The Care Key works just like a standard key when it comes to locking and unlocking, starting your vehicle and most of the other standard actions. The big difference is that you can set a speed limitation for the vehicle when the Care Key is being used. This can be useful when you need to lend your vehicle to an inexperienced driver or give it to a valet or workshop.
When a Care Key with a connected speed limitation is being used, this will be indicated with a symbol in the instrument panel.

The Care Key can also be used without connecting it to a speed limitation. In that case, it works just like a standard key.
Changing the speed limitation setting
The vehicle automatically detects when you unlock it using a Care Key and applies the speed limitation if you have set one.
When you've unlocked the vehicle using a Care Key, you can't change or remove the speed limitation. To access the speed limitation setting again, relock the vehicle and unlock it using a standard key or key tag and select the owner profile.