Political parties in America are organized at the local level, which includes city and county, the state level and the national level. Most democratic countries have many political parties, but the United States has only two major political parties, Democrats and Republicans.
At the local level, candidates run for positions such as mayor, city council or sheriff. These elections are traditionally non-partisan, meaning candidates do not choose to run as part of a specific political party. Candidates are in control of the city or the county in which they are elected. State level elections are held for positions such as senators, state representatives, Attorney General, governor and Secretary of State. State level elections are not non-partisan, meaning candidates choose a political party with which to be affiliated.
These elected officials are either chosen to represent the state at a national level, or they are given certain responsibilities of the state in which they were elected. During national elections, candidates generally split up into one of two major parties, democrats or republicans. Each of the two major parties have a national committee. These committees do not run their candidate's campaigns but they are major supporters of their candidate. There have been candidates from other parties who have run for president, but there has never been a president elected outside of the two major US political parties.