After you have mark your selection out, you can export it as a standalone file now.
is the export button, after click it, a form will display like this:
You can change export sound file type here, for MP3 or WAV format. If you select MP3 format, you can change the compress bit rate. if the origin file format is MP3, you can select "As Origin" to use the bit rate of the origin MP3 file to compress.
After click this button, it will ask you for the file name of exporting file.