Key card in your pocket. Walk up to car, press "request" button. If key card in range, doors open. Depending on number of presses of request button, driver's door, all doors, all doors and trunk, or all windows open.
Can also open windows remotely from outside of car with key card. You might be able to remote start as well, but I haven't read that part of the manual yet.
Sit in car with key card. Turn start knob. If key card in range, car starts. If not then nada. If you take your car to valet parking, take start knob cover off. Give valet special valet key. Different from emergency master key kept within key card. Valet key can only open driver's door and start car. Valet key cannot open trunk or glove box.
If key car left in car and person walks away doors do not automatically lock, but after certain time period key car deactivates itself so that car is then immobilzed with that particular key card. It will start with the back up key card, but the first key car would need to be reprogrammed by Mazda.
R