Turn on Bluetooth on your phone and set it to discoverable, then use the Menu button on the Mazda3 audio screen to scroll through to BT Setup. Select BT Setup using the volume dial, then use that same button to select Pair Device. The system will display a four digit PIN on the screen, accept that by pressing the volume button. The screen should then flash Pairing on the screen, so select the car's Bluetooth name on your phone, then enter the four digit PIN on your phone. The car's audio screen system should show Pair Success if it works as intended. Further details will be in your owner's manual.