It doesn't have to be all that formal. We need to know what your skills and experience are, but it doesn't have to be all neatly formatted and laid out (unless that is relevant to the job you are applying for). A simple letter explaining why you want to help and what you think you can bring to KHTI is sufficient. And, yes, it is necessary. We need to know who is working for us and in what capacity. Certain aspects of our insurance coverage demand this.