Hi Namrata,
Six Sigma as a career is build in various stages called Belts. For understanding the concepts and practical application of themes/tools one should go through Green Belt Training and do relatively less complex or functional related projects (this all can be done with the help of concerns like benchmark. Once this is done the next step is Black Belt Training and certification. Black Belt is generally in my experience the change point from were one can shift his or her career towards more dedicated six sigma role.
One more thing to understand is that not all of those who are six sigma experts, start their career as six sigma professionals, in fact, most of them work in and emerge from different profiles and then pick up six sigma knowledge with their generic expertise. What is more important is STARTING the journey.