Connect the audio output from the cassette player to the line-in input of the computer. If the cassette player has both RCA and headphone jacks, use the RCA jacks for superior sound quality. Most computer sound cards have color-coded jacks; the line-in input will be light blue.
Run Audacity. Click "Edit"; then click "Preferences." Click the "Quality" tab, and ensure that the default sample rate is set to 44100 Hz and that the default sample format is set to 16-bit. Click the "File Formats" tab, and ensure that the uncompressed export format is set to WAV (Microsoft 16-bit PCM). These settings will make your resulting recordings directly compatible with the CD audio format.
Click the red "Record" button in Audacity, and play your cassette. If your equipment is connected properly, you will hear the music through your computer's speakers or will see the level meters in Audacity flicker. If the level meters are consistently maxing out, decrease the volume of the cassette player.
Allow the recording to continue until the entire side of the cassette is complete; then click the yellow "Stop" button in Audacity. You will be left with a single large audio recording.
Click "View"; then hover your mouse over "Set Selection Format." Ensure that "cdda min:sec:frames 75 fps" is selected.
Click "Edit"; then hover your mouse over "Snap-To." Ensure that "Snap On" is selected.
Play your audio track. When you reach the end of a song, stop the playback. Click where the recording has stopped. This will place a vertical line under your cursor.
Click "Edit." Hover your mouse over "Select," and click on "Cursor to End." Click "Edit" again and click "Split." This will split your recording into two files. The first will be your finished first track, and the second will be everything that remains from your original recording. Repeat steps 7 and 8 for each song.
Click on the first track. Click "File"; then click "Export as Wav." Give the file a logical name that denotes its track order, such as "MyFavoriteTape01." Do this for each of the tracks that you have created, ensuring that all of your tracks are saved to the same folder. Your full cassette is now backed up and ready to be burned to a CD.
Open iTunes. Click "File"; then click "New Playlist." Give this playlist a name such as "My CD." You will now see this playlist on the left side of the screen.
Browse to the folder where your recordings are saved. Drag each of these recordings to iTunes, dropping them onto your new playlist. After you have done this, click on the playlist. You should now see all of your track names in the primary iTunes window.
Insert a blank recordable CD into your computer. Click "File"; then click "Burn Playlist to Disc." Your CD will begin to burn. When it is complete, you will have a full copy of your original cassette. If you take care of the CD, it should last for many decades to come.