In Ancient India that is before 3000 years, people were classified based on their castes. Four main types of classes are mentioned:
Brahmins, they would usually serve as priests in the temples, and they would also act as wise gurus to the kings and the learned people.
Kshatriyas would serve as warriors, kings and ministers, Vaishyas, would own farm lands and would be bosses in their business establishments, and Shudras would serve as a labourer or as attendants to the kings and to the wealthy people. Each class insists the people to follow certain rules and regulations.
The details about the various classes of people are mentioned in the ancient Rig Veda.
The caste system in ancient India preserves the purity of the caste, and it was widely accepted by most of the people in India. According to ancient customs and traditions, A Brahmin must have to behave only like a Brahmin, and he should not act like a Kshatriya or a Vaishya since it would hinder him from attaining salvation.
In ancient period, Brahmins are highly respected by the other classes of people, and they are considered as the form of the Vedas, due to their pious nature. A Kshatriya also is supposed to act as per his own class, and he should not behave like a Brahmin. The same thing is applicable for Vaishyas and Shudras also.
But nowadays, a Brahmins are also doing their own business, and some Brahmins are engaged in tannery business also, since it all depends on their own choice. And nowadays, all classes of Hindus have got the privilege to enter into any Hindu temple premises and worship the god. But right now, some people are unnecessarily criticising our SANATANA DHARMA, and they are also finding fault with our ancient Manu Dharma.
Manu Dharma was written by the holy Lord Manu, who is one of the foremost sons of Lord Brahma. He would have written it based on the guidance of Lord Brahma. Hence, Instead of unnecessarily finding fault with our Holy Hindu Texts, let the critics study those things fully, and then they can clarify their doubts with the learned scholars or from the pontiffs of the Hindu Mutts.