Oh - sorry. I think I misunderstood the question.
Simply: You plug some sound source into your computer's sound card (on the rear). Then you start some software to record from that input plug (you won't be able to avoid any of these steps without a DAT recorder). The sound (waves) is digitalized (digitized?) by means of hardware on the sound card. ANY sound - also what is only created by electromagnetic interference.
Any recording software I know will first try to write that incoming digital sound to a so-called WAV-file first. That's some very common format for encoding. Also any software you start afterwards in order to write that sound to a CD will first ask for a WAV file as a source. So - this conversion to and from WAV files was what I meant when I said "without further effort". Of course I also don't know any means to create a CD from sound fed into the sound card 'on the fly'.
One should also mind that every song takes about ten megabytes of disk space for the WAV file, and the computer should at least be some Pentium version for speed. I am also quite satisfied with the quality of the sound I am recording, but - yes - I can hear my computer working and that may be prohibitive for professional purposes.