Install the Audacity program and install the soundcard or connect the external ADC to the computers, per the instructions that come with the unit.
Connect the analog source to the inputs on the soundcard or external ADC. These inputs are usually either RCA-style plugs, 1/4-inch instrument style plugs, or XLR microphone-style inputs.
Select the sample rate. If you are using an external ADC, like many professional audio studios use, select this on the converter. For a CD, the sample rate would need to be 16 bits at 44.1 kHz, which is the Red Book standard. Many professional studios select 24 bits at 96 kHz to get more headroom. Many professional soundcards and audio interfaces allow to select the sample rate through the drivers in the computer; if this is the case, choose the sample rate that way.
Select the sample rate in the recording software and match it on your soundcard/audio interface selection. If you have different sample rates, the audio will not record properly.
Select record in Audacity and start playing the analog signal. Audacity will record the digitized music and let you store it on your computer. Burn the recording to a CD with iTunes or a burning program such as Nero or Roxio.