Dear aspirant ,

To get into IIM'S , they have a overall rating system which will decide for an individual to get into IIM . They have a system like : A+B+C   where A is your std 10th marks , B is your 12th std marks and C is your graduation marks. Then your next stage would be selection for Personal interview (PI)  and Written ability test (WAT) . Then your final selection would be based on the final composite score you obtained . If you have any work experience than that would also be counted and will be a major advantage for you .

Here is the link for detailed criteria about IIM'S admission : https://bschool.careers360.com/articles/iim-admission-criteria

Here is the another link for more information  : https://www.iima.ac.in/web/pgp/apply/domestic/admission/selection-process