In the modem us political system, what is the main system political parties use to nominate candidates. primary caucus general election party appointment

N the modern US political system the main system that political parties use to nominate candidates are primary elections, however, caucus' are also used in certain states. In a primary the vote is cast by a secret ballot in order to decide the candidate of the party. In a caucus members of the party meet in an open meeting and discuss who they will select to be the party candidate for that state.