The easiest way would probably to get some readers/writers pre-made (i.e. buy one).
Many of those have simple interface to PC. Of course, the easiest ones to use would be one that use RS232 comm, but those would probably be the oldest (do they still sell those?). Now, you probably will more find USB, which is of no use in a micro-controler project.
If you wish to learn around the PC keyboard protocol, there are many barcode readers that plug into the keyboard port. When you scan a code, it simply send the scan codes as if you were typing them on the keyboard.
So, from a micro-controler, it would be the same as testing with a keyboard. Note though that when you type something on a keyboard, the code sent by the keyboard is not ASCII, but a specific scan-code for each key. Though, those are well-documented.