Answer:
The major political parties are organized at the local (usually county), state, and national levels. Party leaders and activists are involved in choosing people to run for office, managing and financing campaigns, and developing positions and policies that appeal to party constituents. The national party organizations play key roles in presidential elections.
Local party organization
Political parties operate at the local level in municipal and county elections (though many cities choose officials — mayors and members of city council — through nonpartisan elections, in which candidates effectively run as independents without party affiliation).
Tate party organization
Political parties prepare for statewide elections. Party activists are named as electors in the Electoral College if their party carries the state in a presidential election. Candidates for state office may be chosen through a primary election, state convention, or caucus process. At a state caucus, party members select their candidates. In many states, the executive officials — governor, lieutenant governor, treasurer, and attorney general — are elected as individuals.
National party organization
At the national level, political parties run candidates for Congress and the presidency. Each party has its own national committee made up of party leaders, elected officials, and the chairs of the state party organizations. The chair of the national committee is chosen by the party's candidate for president. The Democratic and Republican national committees do not run the campaigns of their respective presidential candidates; they play a supporting role to the campaign organizations of the candidates themselves. In both the Senate and the House, each party has its own congressional campaign committee, which raises money for congressional elections.