Ideally you'll need a cassette player with a phono outputs (such as the ones found in 'hi-fi separates' systems). But you can also use a cassette player (such as a Walkman) with a headphone socket, as long as you remember to keep the volume set to a fairly low level.
Then you'll need a lead to connect your cassette player to the 'Line In' socket on the back of your PC. (So that's probably either a twin phono to 3.5mm stereo jack lead, or a 3.5mm stereo jack to 3.5mm stereo jack lead). Your local branch of Maplins can supply a suitable lead.
Once you've found a way to get the audio signal into your PC you need some suitable (free) software to record the signal. Audacity is the most popular program:
http://audacity.sourceforge.net/
When you've recorded the audio as a WAV file you can use the CD burning software on your PC (e.g. Nero) to create an audio CD.
Chris