My question is that is it possible to input the rfid tag numbers in the arduino without requiring an external memory like the PC.
Yes, if the number of tags is small.
char tag1 = "ValidTagNumberHere";
char tag2 = "AnotherValidTagNumberHere";
if(strcmp(thisTag, tag1) == 0)
// tag1 was scanned
else if(strcmp(thisTag, tag2) == 0)
// tag2 was scanned
Providing a tutorial as to how to use a specific RFID reader is not possible without knowing which RFID reader you have. Besides, what's wrong with you googling?