Write an article based on this "Connect a cable. Select Line In as the recording source."
Connect a cable with a mini-plug from the line out of your sound card (the green port) to the line in (blue port). Note that all sounds from your computer will be recorded, including system sounds like beeps, alarms, and alerts. You may wish to disable these before recording. Use a single-to-double stereo adapter on the output port, then plug a single-to-single stereo cable from one side of the adapter to the input port, and a pair of headphones into the second side of the adapter, so you can monitor what you're recording.