Hi,
This has been asked before but here goes anyway.
Install some audio recording software such as the free and excellent Audacity.
http://audacity.sourceforge.net/
Once you have set that up onto the connections. Most pc sound cards use stereo 3.5mm jacks as inputs , but some more expensive ones use phono connections. Check on the back to make sure.
For the source you can use either a hifi ( phono plugs )or portable cassette ( 3.5mmjack )or if you want to splash out a usb type which will connect to the usb port of your pc. This will come bundled with software and full instructions.
http://www.maplin.co.uk/Search.aspx?menuno=845 27
http://www.maplin.co.uk/Search.aspx?menuno=845 26
http://www.maplin.co.uk/Module.aspx?ModuleNo=2 20602
Connect the tape deck to the pc and make a test recording, setting levels as required.
Record each track ( piece of music ) individually rather than side 1 tape 1 etc. Takes more time but will be easier in the long run.
Audacity will save the tracks as wav files with are uncompressed. You can save some space if you save them as mp3s (for which Audacity will need the Lame 3 codecs). If you only want to listen to the resultant cds on a computer, just copy the mp3 files to the cd. If you want to make an audio cd use Nero or similar which will do the conversion for you.
http://www.nero.com/enu/support-downloads.html