In addition to the answers, I want share something:
https://www.scirra.com/arcade/tutorial- ... pick-13549
In this example with sample CAPX you'll be able to learn how to deal with UID and how to pick it, also, how to filter conditions using it and achieve anything you want to manipulate the desired object.
For example, you want the player picking the right car? Simple, on collision with this car (trigger, not a permanent checking) set it's UID to the Global variable.
Now you're able to pick this car by filtering it in the condition.
Condition: Pick by Evaluate -> Car with Car.UID = GlobalVariableCar
So, you want its X and Y to update the player position inside the car? Improve with.
Condition: Pick by Evaluate -> Car with Car.UID = GlobalVariableCar
Action: Pin Player to Car;
(it will pin the player to the car, better than using resource with updating every tick, who will consume your CPU more than pin, also, pin have priority over updating position)
or
Action: Set Player Position to Car.X,Car.Y;
(Don't worry, when you filtered the car UID, it's dealing only with him, but avoid update something everytick, use pin instead, it's more efficient)
That's it.