With the bluetooth turned on your phone and sitting in your car, you need to enter the set up mode of your car's bluetooth. This will be in your car's Owner Manual. Follow the steps and this should end with the "Connection Complete" phrase either displayed or spoken.
After this, press the icon (usually on the steering wheel) to access the hands free phone and say "Call". (or whatever it says in your car manual) and the rest should be simple...
Having said that, I can't get voice recognition of names in my phonebook on my car's bluetooth. I have a 2010 Kia Forte and my old phone (an HTC) worked flawlessly, but the Galaxy Q - not so much.

Drag down from top of the screen to open the notification window. You should see a button to activate Bluetooth. Another way is to press the Home button > Menu > Settings > Wireless and networks > Bluetooth.

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