You can't join MBA course just after 12th board ,for MBA course you should have to appear for graduation course and after that you can appear for MBA course as well as exam.For MBA course you should fulfill certain eligibility criteria.First of all you should have a Bachelor's degree of atleast 3 years for MBA course.you must have at least 50% in your final exam of graduation.

Hello

The eligibility criteria for pursuing MBA is that a candidate should have passed graduation in any discipline from a recognized university.

So, a person with 12th passed qualification evidently cannot apply for MBA course, since it's a Master's Degree Program.

However, there are institutes which provides integrated MBA courses, if it interests you,you may consider that. Like, in case of IIM Indore which provides five year integrated course in management.