Answer
In the system of separate electoral, the government divided the country's territory into several districts. Each districts are given to a community based on a certain characteristics (could be based on caste, religion, or ethnicities). The people from each district could conduct their own election and select the representatives from their district.
In the system of the reservation of constituencies, each district have their own candidates to be elected within the parliamentary or state assembly selection. But they need to accumulate their votes from all voters in India.