For editing down a song in audacity, my very crude process is as follows:
1-load song (original) FILE-->OPEN (select your audio file)
2-listen to song and use zoom in/out to focus on a fairly tight range if needed -- you might decide on a target length or just evaluate which sections you could remove and still get a new song that you like.
3-highlight sections you want to remove with mouse (highlight waveform with mouse selecting left to right side)
- you can listen to the selection before deleting to make sure you nailed the part you want to remove
- adjust as necessary by moving starting or ending range of selection with mouse, a finger appears as you adjust either side
- finally you happy with the range selected for removal
4-click delete to remove
5-now click the waveform "just before the beginning of deleted section " and listen (play it) to the transition ... often you need to adjust till it sounds right or is "on the beat", etc.
- if you don't like it, then undo the delete (CNTL-Z) and modify selection, then re-delete, re-listen, repeat till you like it, undo is your friend, re-adjust selections you remove.
6-once you are done removing sections, you may need to add a fade out effect at the end
7-FILE--> EXPORT (selection new name and format)
