Download and install Audacity (audacity.sourceforge.net).
Plug the male side of both RCA cables into the matching female connectors of the cassette tape deck labeled "Line Out" or "Audio Out."
Plug the mini-jack connector into the line-in jack on your computer.
Open Audacity.
Click on "Edit" at the top of the screen, scroll down and click on "Preferences."
Click on the drop-down menu for "Device" under the "Recording" heading and choose the device that matches your line-in device. Click on the "OK" button.
Press "Play" on your cassette deck to monitor input levels.
Click on the downward-pointing arrow under the red recording level meters to adjust the input volume.
Stop and rewind your tape to the correct starting position.
Click the "Record" button in Audacity, and press "Play" on your cassette deck.
Click the "Stop" button in Audacity to stop recording. Press "Stop" on your cassette deck.
Click on "File," scroll down and click on "Save Project As."
Enter the desired track name into the empty "File name" text field and click on the "Save" button to save the cassette music to your computer.