The RFID module available on market which is RC522 (MFRC522) module is based on SPI port. One pin on SPI port is slave select or SS which is used to select a particular module by a pin and use that to read cards. Please refer to widely used Github library for arduino https://github.com/miguelbalboa/rfid .
However RC522 is not fully working with NFC. NFCs are just a step ahead of RFID in technology. However there are PN532 modules in market and you can use those with Arduino. Goodluck