Retreiving and Passing data or signal from PC to ArduinoUno

Okay, so I am trying to do a project, where I read data from an RFID reader to the Arduino, the Arduino will pass it to a PC , where an application will check a database if this RFID tag is allowed or not, and then the application will send back a flag to the arduino for yes or no.

So my question is first, how to make the arduino to pass information to the PC ? To get it from the RFID reader, I guess I have to use Serial.Read from here - Arduino Reference
And second, how to make a C or C++ application to pass information back to the Arduino ???

Arduino to PC:


C/C++ in PC to Arduino: don't know.