Question

what was the diwani right ?how it helped the british to set up their control in india ?

Answer 1

In 1765, the Mughal Empire appointed the company as the Diwan of the provinces of Bengal. The Diwani allowed the company to use the vast problems that the company faced earlier. From the early 18th century its trade with India has expanded. But it had to buy most of the goods with gold and silver imported from Britian. This was because at this time Britain had no goods to sell in India.
The outflow of gold and silver slowed down after the Battle of Plassey and entirely after the Diwani Rights. 
Revenues from India could finance Company expenses. These revenues could be used to purchase cotton and silk textiles in India, maintain Company troops, and meet the cost of building the company fort and offices at Calcutta.

Answer 2

Diwani is revenue collection. In 1765 , the mughal emperor appointed britishers as diwan. This helped them alot. the supply of gold and silver from england stopped. they started trading with indians with the money of indians.