An SOP or better known as a Statement of Purpose is an essay which a student has to write for the admission process at a university. It is a long essay which contains the personal story of the student about his career so far, future goals and how joining the university will help him in achieving those goals. It is unique for each student and thus the student has to personalize it. Also, for every different university that you apply to, you have to write a unique statement of purpose.
Check out some general strategies which the students can follow to write an SOP which impresses the members of the admissions committee.