What computer operating system is your Premiere Elements 12 running on? Please be sure to update 12 to 12.1 in an opened project's Help Menu/Update.
Yes, you can use your own music in Premiere Elements 12/12.1. However if you have iTunes music, you will probably find it necessary to convert the m4a into wav in iTunes before importing the music into a Premiere Elements 12/12.1 project. Do you know how to do that conversion? If not, I will supply you with a step by step How To.
Suggested resources (for starters)
1. See the Expert Guided and Quick Guided Edit workspaces and the several lessons there.
2. Help PDF
Premiere Elements 12
Elements Organizer 12
3. Adobe TV
Please review and consider. Any questions or need clarification, please do not hesitate to ask.