Connect your cassette tape player's headphone jack to your computers line-in jack using the 3.5mm audio cable.
Launch the free audio recording software Audacity.
Set Audacity's input to "Line-in."
Click the red "Record" button in Audacity, and press the "Play" button on the tape player.
Click the "Stop" button in Audacity once the tape has finished playing.
Click "File > Export as WAV" to export an audio file that can be imported into your favorite audio management program (such as iTunes) and loaded onto an iPod or burned to a CD.