INSTALL AUDACITY & LAME MP3 ENCODER. Both files can be both on Audacity's website. You need to install the Lame MP3 encoder as well, otherwise you won't be able to export any of the MP3s that you edit. Instructions to do so can be found on the site.
OPEN THE MP3 IN AUDACITY. Once both files have been installed, open Audacity, then go to File -> Open, and select the MP3 you want to edit.
EDIT THE MP3 by selecting the area you want to delete (click and drag over it with the cursor). Then press Delete on the keyboard to remove that section from the MP3.
EXPORT THE EDITED MP3. Once you've done all the editing you need, it's time to export the MP3. Select File -> Export as MP3, then give the file a name and choose a place to export it to finish.