Varna, Caste and duty in the Bhagavad Gita

The word Varna determines a group of people in the society, where we are bound to each other in a same group. Bhagavad Gita says the concept of Varna decided on the basis of our action as it is prescribed by the society. Varna is divided on numbers, that is four Varna (Brahmana, Kshitra, Vaishya, Shudra) and it determines our body color. On the other hand Caste is a small group of people where there is no mobility like Varna, though it has sub - castes. Caste is based on local ritual and occupation. So, both are slightly co related to each other. Both are based on action. In this paper I would like to explain the duty according to Varna and Caste. In addition, also I would like to explain the duty as Bhagavad Gita says. And there will be a study that, is it possible to implement or not in our practical life.