Your sound card normally has two input connections,
one labeled "Line", one labeled "Mic". It also has one output
connector, for a line level or headphone output. Unfortunately, all of these jacks look
exactly the same, but they are often labeled (you may have to look closely). You want to
find the Line In (or just Line) jack for the best sound. If it's not labeled, you can
consult your system documentation or just work by trial and error - when you see how to
monitor input levels in the mixer, you'll easily be able to tell whether you're plugged
into the right input or not.
The input jacks for sound cards are typically
stereo 1/8" mini-phone plugs.
Then choose a sound source. This can be a cassette
player, a CD player, or a stereo component. Receivers and mixers are good sources to tap,
as a single connection gives your computer access to several devices.
If your sound source has a Line Out jack, use it to
connect to the sound card's input. If your sound source has only a headphone jack, it will
do (Line Out jacks generally have higher sound quality, and an optimum level. The level
coming out the headphone jacks is affected by the headphone volume control; Line Outs are
independent of this volume control).
The source may have a single stereo 1/8"
mini-phone jack like the sound card, or it may have a pair of RCA jacks or other