Firstly they are selected by the election commision by checking if they are above the age of 25 yrs , if they have criminal background or have a sound mind.
then they stand for election , electiion campaign takes place where they give out decisions and policies and tries to get maximum support from citizens
after that , the day of election is announced whenthe campaign stops.and finally the day of polling where the eligible citizens caste their vote in favour of their candidate choice.

Generally speaking, India is a democracy and candidates running for presidency or other posts are elected by the people.
India follows a government that is run by the people and for the people.