Download the audacity program for free at the Audacity website, found in the resources section. Run the downloaded application and install the program.
Plug the cassette player into the computer's microphone entry with the male-to-male stereo cable by placing one end of the stereo cable in the cassette player's headphone outlet and the other end of the cable into the computer's microphone input.
Start Audacity and change the input type to "Line in" or "Microphone" on the drop-down menu at the top-right corner of the screen or in the "Preferences" menu under "Devices."
Push the record button on Audacity, then press play on your cassette tape. Push the stop button on Audacity, then the stop button on your cassette player when finished.
Click the file menu in Audacity and select "Export as WAV." Name your file and click "Export." Close Audacity.
Open iTunes and add your ".WAV" file by clicking "Add to Library" in the "Files" menu. Click "Preferences" and then click "Import Settings." In the "Import Using" drop-down menu presented, select "MP3 Encoder." Return to the main iTunes interface by clicking "OK." Find your ".WAV" file in the library and click on "Advanced" at the top of the screen. Select "Create MP3 Version." The conversion will take a minute to complete.