How do political parties determine and shape public policy

Political parties are elected by the people who represent the citizens of a country. The political parties that have power determine and shape the public policies. The question is which party, and that depends on the party that has won the elections or the ruling party in power. If a bill has to be passed, the majority of votes are required to pass the bill or to implement or execute the policy. Public policies are framed based on certain norms which, are adhered to. The norms are complied with by the parties to make sure that the public policies are in accordance with the public opinion. Political parties and elected authorities indeed represent and shape public policies that can be compared to a family and head of the family making decisions for the family.