Convert cassette tapes to mp3s using Garage Band 6.0.5?

I bought a program for a cassette tape to mp3 converter, but it didn't work and the customer service was a nightmare.

I can connect a walkman to my computer through a USB cable. I've never used Garage Band 6.0.5 before, so I was just wondering if it's possible to do this and if so, can someone give me a step by step guide since I'm a novice?