Help with RFID Module

I tried connecting my RFID unit to my arduino and running the code in libraries but i got this error message.

Libraries/rfid/examples/ReadAndWrite/ReadAndWrite.ino:31:21: fatal error: MFRC522.h: No such file or directory
#include <MFRC522.h>
compilation terminated.
exit status 1
Error compiling for board Arduino/Genuino Uno.

You can’t just copy a sketch without downloading the proper library. If you did download it, you did not properly install it.