Yeah, speakers OUT (or LINE OUT) are usually marked as light green circles around that little hole... not always, but on most new cards it's like that...
If you have sound card with 2 lines out, one is for front speakers, one is for rear speakers. If you plug your speakers jack into rear speakers line out, and you don't enable QUADRAPHONIC SPEAKERS feature from Speakers settings in SOUNDS, SPEACH and AUDIO DEVICES, you won't hear anything...
Anyway, if you are using just 2 desktop speakers, choose DESKTOP STEREO SPEAKERS from the same menu...
Cheers !