Question

why is election necessary for democratic country

Answer 1

or is necessary because election is a powerful tool of it and democracy cannot be useful without it

Answer 2

Elections are important in a democracy as it lead to political and social stability in a country. 
People choose their representatives ( leaders ) in an elections, everyone in a country is not capable of taking decisions nor they have time or knowledge to take decisions so in elections people choose their decision makers whom they think would work for the welfare of the country.

Elections are important for, Free and Cheap Education for all.
Elections are important for, No corruption.
Elections are important for, Good Roads.