In order to get admission in the MBA course in IIMs you first  need to have a Bachelors Degree, with a minimum of  50% marks or equivalent CGPA. You should  appear for CAT/GMAT Exams. Then , later based on your score, You will be shortlisted for personal interviews. The admission depends on your marks in Academics also, where 70% weightage is given to your CAT/GMAT score and  about 30% weightage is usually given to the Application Rating Score.