Hello Y.Dheivanai , If you want to do MBA after your B.Com, You have to take either National Level MBA Entrance Exam or State Level MBA Entrance Exam. If you want to apply for MBA Entrance Exam, You should have minimum eligibility criteria those details are as follows :

A Candidate one who want to apply for either state level or national level MBA entrance exam that candidate should obtained Bachelor's Degree with minimum 50% of marks (45%of marks for SC/ST) from recognized university can eligible to apply for MBA entrance exams 

National Level MBA Entrance Exams: CAT, CMAT, XAT, SNAP, GET, MAT etc..

State Level MBA Entrance Exams: Maximum Every state has a separate MBA Entrance Exam,
-->> TANCET for Tamilnadu
-->> ICET for Andhra Pradesh
-->> PGCET for Karnataka etc..

For MAT entrance exam, Graduation in any discipline from recognized university can eligible to apply for MAT.

MBA entrance exams consist following sections those are as follows Quantitative Aptitude, Logical Reasoning, Verbal Ability, Data Interpretation, Data Sufficiency and General Knowledge etc..

So you have to prepare for Quantitative Ability, Logical Reasoning, Verbal Ability, Data Interpretation and General Knowledge .

Admission procedure for MBA colleges is as follows Written Test, Group Discussion and Personal Interview. So you have to prepare therese rounds for to get a admission in MBA course.

I hope this would be useful.