The primary election process ends with the national conventions of the political parties. Once the national conventions have been held, and the candidates from the political parties have been nominated and chosen, the presidential election begins in earnest as a contest between the candidates from the political parties.
Some people choose to run for president without being affiliated with a political party.
Such independent candidates need not concern themselves with getting nominated by a party, but must meet other requirements. For example, such candidates are required to collect a large number of signatures to support their nominations. The sources of funding used by independent candidates comes from personal funds and loans as well as fundraising campaigns. The candidates campaign right up until Election Day, when the nation finally votes for its President. The candidates travel throughout the country, making public appearance and giving speeches.