To do so in A. Audition you just need to highlight the end (or begining) with a mouse end press delete button on you keyboard.
Save your changes and job is done.
Adobe seems to be complicated at first but it is worth a try.
You can fade in fade out, add the effekts like echo. digital delay, compresion,
Dynamic and others Eq. etc etc.
You can make mono, stereo or 5,1 surround audio files.
I suppose you did not double click on your mp3 to get to Adobe edit window.
I use other Adobe Audition, A. Photoshop, A. Premiere and A. Encore.
These 4 together helps me to make great home videos.
Still I use Nero beside them because Nero is great.
It is just matter to choose the right program for needed aplication.