Plug an audio cable into the cassette-tape player's line-out jack, sometimes also called a headphone jack. This is usually either a 1/4" phono jack or 1/8" headphone jack. Plug the other end of the audio cable into the computer's line-in jack.
Download and install a free audio-recording program such as Audacity, Wavosaur or Kristal Audio Engine. Run the recording program and make sure the input type is set to "Line in" by selecting "Preferences" from the Edit menu. Use the "Device" selector to select "Line in" as the input. Click "OK."
Click on the large red record button in the main program window to begin recording a new audio file. Press the "Play" button on the cassette deck to begin playing the tape into the computer.
Allow the tape to play in its entirety as the software records the input. Press the "Stop" button in the recording-software program when the tape has finished playing.
Click "File" and "Export as WAV" to save the recording as a digital file on the computer. Select a destination path and enter a file name and then click "Export" to save the file.