Career making is generally started early during school days when aspirations for a particular stream or line are generated in the mind. A student accordingly chooses his subjects and tries for the career line like teaching, engineering, medical, competitive exams etc. By that time he also knows his interests and aptitude which focus a person in a particular path.
In your case willingly or unknowingly you have reached Post Graduation in Mathematics and now are not clear what to do. It means you did not have any firm aptitude or interest in your mind for your career.
Anyway, let us not worry for past and now concentrate in the present and plan for future. First of all you asses your academic capabilities and your grading in the earlier classes and expectation in present course. If it is good go for some top ranking competitive exams in our country which will place you in the best of careers today. Why I am emphasising on your so far achieved academic excellence is because if you are having good grades you can expect to score more marks in these coveted examinations like Indian Administrative Services, State Civil Services, Baking Services etc.
If you are not confident of your academic potential then you have other ways to select a career line by going for diploma courses in areas of your interest like computers, finance, management etc and then try to apply for jobs in various industries and organisations. There are other options like subordinate services in Govt establishments, Postal services, Railway services and openings in many public sector undertakings.
Have you got interest in academic and theoretical research? If so, Mathematics is a great subject to pursue it and you can get a PhD degree which will make way for your applying to coveted institutes like TIFR, IISc, IIT etc of our country for further research work.
Do not think that by doing PG in Mathematics your capabilities are limited. In fact there are many Mathematicians who are the best computer programmers today in the world.
So you might have to go for some courses in finance , management or computer related fields before you apply to the relevant industries for jobs. Do not sit idle after your PG. Join any job even if it does not interest you. The reason is during a job you acquire many skills and experience which help you to get another job quickly. Sitting idle will be rusting the existing knowledge.
Have you interest in business, marketing, transport and allied areas? These are the areas where degrees count less than the practical and common sense approach and many young people have carved a career for them selves in these paths. It is true that sometimes a single person can not start a business but you can join some group of people who are already innovating and enterprising in different areas and you can learn a lot with them. Initially hardships will be there as they will not be able to pay you much but later when the business makes a place in the niche market more opportunities and prosperities are generated and you can continue with them or think of starting something on your own.
So consider different options vis-a-vis your capabilities and capacities to work hard and there is no reason why you can not shape your future career.
Knowledge is power.