If you’re wondering why we used SoftwareSerial – if you connect the data line from the RFID board to the Arduino’s RX pin – you need to remove it when updating sketches, so this is more convenient.
Now start waving RFID cards or tags over the coil. You will find that they need to be parallel over the coil, and not too far away. You can experiment with covering the coil to simulate it being installed behind protective surfaces and so on. Watch this short video which shows the resulting RFID card or tag data being displayed in the Arduino IDE serial monitor.