    *NOTE to the author     there is a big difference between the two parties. Democrats are more liberal and Republicans are a lot more conservative.       Note to the Note   The question was related to the PARTIES, not the philosophy of individual members.
It works like this: a political party through its manifesto says-if you vote for me then I will do this for you. Uses: 1. Canvassing of vote for political parties 2. Helps people to decide which party to vote for 3.
FYI - A primary election (nominating primary), also referred to simply as a primary, is an election in which voters in a jurisdiction select candidates for a subsequent election. In other words, primary elections are one means by which a political party nominates candidates for the following general election.