Here are some basics that might be helpful:
-Music therapy is research-based, looking at the effects of music on movement, communication, relating to others, and cognition.
-Music therapists work with premature babies in the NICU to the elderly in hospice. Therapists work in forensics, neuro or drug rehab, schools, hospitals, and much more.
-Music therapists assess clients, create goals based on strengths and needs, and document progress.
-In order to become a music therapist, one must attend a rigorous undergrad or graduate program that includes study of music, psychology, music therapy, and 2 years of fieldwork at different sites. Students intern for six months (1000 hours) and take a Board Certification Exam.
-There is a good article that gives examples of how music therapists apply their skills written by Ronna Kaplan, former president of the American Association of Music Therapy (AMTA), here. The AMTA website also has much more information, here.