What version of Premiere Elements are you using and on what computer operating system is it running?
Music can be imported from its computer hard drive location into the Premiere Elements workspace (See Add or Get Media/Files and Folders) and put on an audio track such as the Soundtrack. If your music source is iTunes (m4a), you would want to convert that m4a to wav or mp3 in iTunes and then import the wav or mp3 file into the Premiere Elements project.
Please supply details as to program that you are working with and you intended end product. Later versions of Premiere Elements can burn its Timeline content to AVCHD as well as DVD-VIDEO format on a DVD disc.
In future discussions on your question, we may get into program features such as Audio Mixer and Smart Mix. But, that for another time when we are on firmer ground with the details.
At this point, I am not completely sure that you are not in the Elements Organizer Slideshow Editor. Answers will be in the details that you supply.