The RDM6300 RFID module is very simple to use. Connect GROUND and 5VDC from the Arduino to the RFID module. Next, connect the TX pin from the RFID module to a digital input pin on the Arduino. In the example code the pin used to read is pin 2. By setting up the Arduino to read the serial connection on pin 2 at 9600 bps using SoftSerial, you will be able to see the RFID tag number displayed.
The code below reads in the RFID Reader output and compares the received tag numbers to a list of tags in Flash. If the tag number is in the list then pin 7 is set HIGH for a specific duration unlocking a door or performing the desired task.
I found that the RFID Reader module fits nicely into a telephone jack with all the screws and cables removed.