How do you trim the ends of a song.
Editing in Audacity is generally a case of “selecting” the audio that you want to act on, and then applying an action to that selected audio.
The easiest way to select audio is to simply click and drag on the blue waveform. Other ways are described here: http://manual.audacityteam.org/man/audacity_selection.html
It may be necessary to zoom in or out so as to be able to clearly see the part that you want to select. Information about zooming here: http://manual.audacityteam.org/man/zooming.html
Once the audio is selected, you can apply an action to it. For example, to deleted the selected audio, press the DEL (Delete) key on your keyboard, or select “Delete” from Audacity’s “Edit” menu.
You may find this tutorial useful: http://manual.audacityteam.org/man/tutorial_editing_an_existing_file.html