I just looked at the datasheet - this device has no brains - it's just the rf rx & tx. Firstly, you've got to find suitable RFID cards (or devices) that use 125khz. Then you have to get the protocol info - most manufacturers want a NDA and a commitment of many devices before giving this info away. Then you have to implement the signalling scheme and the data transfer protocol. This should keep you busy for a while - not a task for the beginner.

Google my friend.