What version of Premiere Elements and on what computer operating system is it running?
If you are using iTunes music, typically you need to take the music into iTunes to obtain the WAV version which you then import into the Premiere Elements project using Premiere Elements Add Media (Get Media)/Files and Folders.
Even if music is purchased, be sure to check any "right to use" information. Several reports have surfaced about YouTube and Vimeo rejecting video upload for copyright related to music used in video.
Please consider and supply more information for deeper details.