Open the music/track up in Audacity.
Right at the very beginning ( 0 on the scale) place your mouse over it and a hand icon wil appear.
Now drag the hand up to say 30-40 seconds mark-depending how long of the song you want
Now that section should turn blue-ish/grey.
Go to 'edit' at the top and click trim.
Should now show just the trimmed part of the song!
If required:-
Go to '0' on the scale again and drag almost to the end so you have a few seconds left.(last few seconds should now be blue/grey!)
Click 'effects' at the top and 'fade out'
So the song should play and gradually fade out.
Hope that makes sense!