Constitution is a set of rules needed for the proper functioning of a country. We need constitution because it lays down certain rules and ideas by which a government runs. It prevents domination of majority over minority. It safeguards the freedom of the people. 
      If there is no constitution in our country, then there is a chance that our political leaders can misuse their powers and vice versa. 
A constitution is very imp in every country but in democratic country it has more define the political system of the government whether it should be monarchy or democratic,it lays down certain ideals according to which the government of a country runs like secularism,democratic, freedom, justice etc,it gives fundamental rights to the citizens,it describes the powers of different government officials so clearly that there is no clash between them for their powers and positions .If a country don't have a constitution there will be many problems that is the ministers will start misusing their authority, there will be no justice and law all over the country, fundamental rights will not be given to the citizens.