Usually, in an SOP for MS in USA, you start with an introduction where you will talk about your inspirations in life that have led you to apply for this program. You can also start with your short term and long term career goals and how they are aligned to pursuing this course at this particular university. Then you move on to your academic and professional background in length and talk about your expertise, achievements and learnings. This has to be followed by why you have chosen this particular university and how you can contribute to the university in any way. You will also talk specifically about the university and what about it has attracted you. Be very specific here as the admission committee wants to know how well you have researched on the institution.
