Letters of intent may be advanced in the world of commercial real estate. In some specific domestic markets (for example in principal to principal deals between upstream Petroleum traders and producers in the same country, or certain Joint venture projects) they may be found. But there is no underlying and supported standard international application for the Letter of Intent.
In the body paragraph you will basically express your interest in taking admission. Important things you are going to mention include the basis for applying to the school. Why do you think this school can build up your career? List down all academic achievements and special skills that would help in making your letter stand out from rest of the applicants.