Computers now provide a sound as good as any lounge player or HiFi set. You can use your PC to listen to music (including mp3 which restore a sound equal to an audio CD).
However, the sound quality is generally limited by the quality of your PC speakers. If you have a lounge player or HiFi set, then you can try to connect it to your PC.
The audio input/output
An RCA audio input on the HiFi:
It corresponds to an entry named as line in, aux or CD.
The sound card
The sound card of the computer must have one or more outputs. Check the manual of the card where the exit. It can be of two types:
Regular port, in which case a cable like the one below will be needed:
RCA port, also called CINCH (red and white or red and black), in which case it will acquire the following cable: