The best bet would be for you to read
this about using a mixer with a DAW.
Most setups would make use of direct outs on the mixer, but that mixer you have is rather limited in its routing capabilities. It seems as though it only offers one AUX send with a stereo return (your FX Send).
Myself, if I where using that mixer, I would set it up as I had said (Tape Out or Main Out to soundcard). This would give you true stereo separation from each channel going to the computer. I wouldn't be trying to monitor off of the mixer (OCONOR is right in that would create a feedback loop). Instead, I would monitor directly off of the soundcard's Line Out. Which can be done, provided you don't have the Line In in the playback section of the Creative mixer muted. You may even be able to plug the Headphones right into the Line Out of the soundcard (adapter may be needed to go from 1/4" TRS to 1/8" TRS). TRS meaning Tip, Ring and Sleeve .... Or think of it as "Three Ring Stereo" plug, though the proper terminology is tip ring sleeve. Chances are you won't get much volume to the headphones that way, hence others recommendation of a cheap headphone amp. An old HiFi stereo would work in a pinch also.
If you have computer speakers hooked up to the line out .... do they offer a headphone jack? That would work also.
OCONORS method will work, but you will only be able to record MONO tracks, and you will only see levels on one side as you are recording. Once they have been recorded, Acid will allow you to pan them to taste. This won't be true stereo representation, as you have recorded using only one channel of the mixer and sent it to the computer in mono. Again, this is fine for many recordings, but say you someday want to capture the true stereo Image of what you record .... it ain't gonna happen using one channel or all channels, when using just the one FX Send.
If all you ever plan to do is record single mono tracks at a time .... go for it, use the FX Send, set Acid to record mono tracks from the left channel and Pan them at 12:00 to hear um in both ears. While you are recording the tracks, you will only see levels on one channel (Left as you have stated) in Acid.
On a side note: I would like to state that I also am no 12 year old child whom hasn't a clue how to do digital audio recording via computer. I make money doing it.
Thank you and good night.